Electrochemiluminescence (ECL) plays a key role in analysis and sensing because of its high sensitivity and low background. Its wide applications are however limited by a lack of highly tunable ECL ...luminophores. Here we develop a scalable method to design ECL emitters of covalent organic frameworks (COFs) in aqueous medium by simultaneously restricting the donor and acceptor to the COFs' tight electron configurations and constructing high-speed charge transport networks through olefin linkages. This design allows efficient intramolecular charge transfer for strong ECL, and no exogenous poisonous co-reactants are needed. Olefin-linked donor-acceptor conjugated COFs, systematically synthesized by combining non-ECL active monomers with C
or C
symmetry, exhibit strong ECL signals, which can be boosted by increasing the chain length and conjugation of monomers. The present concept demonstrates that the highly efficient COF-based ECL luminophores can be precisely designed, providing a promising direction toward COF-based ECL phosphors.
The hydrolysis of earth‐abundant AlIII has implications in mineral mimicry, geochemistry and environmental chemistry. Third‐order nonlinear optical (NLO) materials are important in modern chemistry ...due to their extensive optical applications. The assembly of AlIII ions with π‐conjugated carboxylate ligands is carried out and the hydrolysis and NLO properties of the resultant material are studied. A series of Al32‐oxo clusters with hydrotalcite‐like cores and π‐conjugated shells are isolated. X‐ray diffraction revealed boundary hydrolysis occurs at the equatorially unsaturated coordination sites of AlIII ions. Charge distribution analysis and DFT calculations support the proposed boundary substitution. The Al32‐oxo clusters possess a significant reverse saturable absorption (RSA) response with a minimal normalized transmittance up to 29 %, indicating they are suitable candidates for optical limiting (OL) materials. This work elucidates the hydrolysis of AlIII and provides insight into layered materials that also have strong boundary activity at the edges or corners.
A series of Al32‐oxo clusters with hydrotalcite‐like cores and π‐conjugated shells were isolated, which are unique models of two‐dimensional or layered materials and may be used to study boundary activity and optical limiting properties.
In this study, we have developed a novel catalyst synthesized by phosphotungstic acid and a gemini quaternary ammonium cation salt. This quaternary ammonium salt not only reduces the interfacial ...tension between olefins and hydrogen peroxide but also forms a notably stable structure with phosphotungstic acid. Dodecene was successfully epoxidized to epoxy dodecane with a selectivity of 82.9 %. The impact of initial conditions was systematically investigated such as molar ratio, temperature, reaction time, and catalyst dosage on the catalytic performance. Characterization of the catalyst morphology was performed by SEM, TEM and SAXS. Raman spectra, FT‐IR and XPS spectra were employed to perform the catalyst transformation during the epoxidation reaction. This catalytic mechanism study could provide the industrial application in the epoxidation of long‐chain olefins.
A novel phase transfer catalyst comprising phosphotungstic acid and biquaternary ammonium cation salt is synthesized for the epoxidation of long carbon chain olefins under solvent‐free conditions, which exhibits high selectivity for epoxides. Different methods are used to characterize the fundamental structure and catalytic mechanism of this catalyst.
Engineering cellular metabolism for improved production of valuable chemicals requires extensive modulation of bacterial genome to explore complex genetic spaces. Here, we report the development of a ...CRISPR–Cas9 based method for iterative genome editing and metabolic engineering of Escherichia coli. This system enables us to introduce various types of genomic modifications with near 100% editing efficiency and to introduce three mutations simultaneously. We also found that cells with intact mismatch repair system had reduced chance to escape CRISPR mediated cleavage and yielded increased editing efficiency. To demonstrate its potential, we used our method to integrate the β-carotene synthetic pathway into the genome and to optimize the methylerythritol-phosphate (MEP) pathway and central metabolic pathways for β-carotene overproduction. We collectively tested 33 genomic modifications and constructed more than 100 genetic variants for combinatorially exploring the metabolic landscape. Our best producer contained15 targeted mutations and produced 2.0g/L β-carotene in fed-batch fermentation.
•Generated near 100% editing efficiency using dsDNA as editing template.•One cycle of genomic editing required only two days.•Strains with functional MMR system yielded increased editing efficiency.•Combinatorially optimized MEP pathway and central metabolic pathways.•Best strain produced 2.0g/L β-carotene using glucose as the sole carbon source.
Covering: up to 2020
As a main bioactive component of the Chinese, Indian, and American
Podophyllum
species, the herbal medicine, podophyllotoxin (PTOX) exhibits broad spectrum pharmacological ...activity, such as superior antitumor activity and against multiple viruses. PTOX derivatives (PTOXs) could arrest the cell cycle, block the transitorily generated DNA/RNA breaks, and blunt the growth-stimulation by targeting topoisomerase II, tubulin, or insulin-like growth factor 1 receptor. Since 1983, etoposide (VP-16) is being used in frontline cancer therapy against various cancer types, such as small cell lung cancer and testicular cancer. Surprisingly, VP-16 (ClinicalTrials NTC04356690) was also redeveloped to treat the cytokine storm in coronavirus disease 2019 (COVID-19) in phase II in April 2020. The treatment aims at dampening the cytokine storm and is based on etoposide in the case of central nervous system. However, the initial version of PTOX was far from perfect. Almost all podophyllotoxin derivatives, including the FDA-approved drugs VP-16 and teniposide, were seriously limited in clinical therapy due to systemic toxicity, drug resistance, and low bioavailability. To meet this challenge, scientists have devoted continuous efforts to discover new candidate drugs and have developed drug strategies. This review focuses on the current clinical treatment of PTOXs and the prospective analysis for improving druggability in the rational design of new generation PTOX-derived drugs.
Natural product podophyllotoxin exhibited superior broad spectrum antitumor and antiviral activity. Over past 30 years, scientists devoted continuous efforts to develop druggability strategies and discover new podophyllotoxin-derived drugs.
Shenlian (SL) extract has been proven to be effective in the prevention and treatment of atherosclerosis and myocardial ischemia. However, the function and molecular mechanisms of SL on coronary ...artery no‐reflow have not been fully elucidated. This study was designed to investigate the contribution of SL extract in repressing excessive mitochondrial autophagy to protect the mitochondrial function and prevent coronary artery no‐reflow. The improvement of SL on coronary artery no‐reflow was observed in vivo experiments and the molecular mechanisms were further explored through vitro experiments. First, a coronary artery no‐reflow rat model was built by ligating the left anterior descending coronary artery for 2 hr of ischemia, followed by 24 hr of reperfusion. Thioflavin S (6%, 1 ml/kg) was injected into the inferior vena cava to mark the no‐reflow area. Transmission electron microscopy was performed to observe the cellular structure, mitochondrial structure, and mitochondrial autophagy of the endothelial cells. Immunofluorescence was used to observe the microvascular barrier function and microvascular inflammation. Cardiac microvascular endothelial cells (CMECs) were isolated from rats. The CMECs were deprived of oxygen–glucose deprivation (OGD) for 2 hr and reoxygenated for 4 hr to mimic the Myocardial ischemia‐reperfusion (MI/R) injury‐induced coronary artery no‐reflow in vitro. Mitochondrial membrane potential was assessed using JC‐1 dye. Intracellular adenosine triphosphate (ATP) levels were determined using an ATP assay kit. The cell total reactive oxygen species (ROS) levels and cell apoptosis rate were analyzed by flow cytometry. Colocalization of mitochondria and lysosomes indirectly indicated mitophagy. The representative ultrastructural morphologies of the autophagosomes and autolysosomes were also observed under transmission electron microscopy. The mitochondrial autophagy‐related proteins (LC3II/I, P62, PINK, and Parkin) were analyzed using Western blot analysis. In vivo, results showed that, compared with the model group, SL could reduce the no‐reflow area from 37.04 ± 9.67% to 18.31 ± 4.01% (1.08 g·kg−1 SL), 13.79 ± 4.77% (2.16 g·kg−1 SL), and 12.67 ± 2.47% (4.32 g·kg−1 SL). The extract also significantly increased the left ventricular ejection fraction (EF) and left ventricular fractional shortening (FS) (p < 0.05 or p < 0.01). The fluorescence intensities of VE‐cadherin, which is a junctional protein that preserves the microvascular barrier function, decreased to ~74.05% of the baseline levels in the no‐reflow rats and increased to 89.87%(1.08 g·kg−1SL), 82.23% (2.16 g·kg−1 SL), and 89.69% (4.32 g·kg−1 SL) of the baseline levels by SL treatment. SL administration repressed the neutrophil migration into the myocardium. The oxygen–glucose deprivation/reoxygenation (OGD/R) model was induced in vitro to mimic microvascular ischemia–reperfusion injury. The impaired mitochondrial function after OGD/R injury led to decreased ATP production, calcium overload, the excessive opening of the Mitochondrial Permeability Transition Pore, decreased mitochondrial membrane potential, and reduced ROS scavenging ability (p < 0.05 or p < 0.01). The normal autophagosomes (double‐membrane vacuoles with autophagic content) in the sham group were rarely found. The large morphology and autophagosomes were frequently observed in the model group. By contrast, SL inhibited the excessive activation of mitochondrial autophagy. The mitochondrial autophagy regulated by the PINK/Parkin pathway was excessively activated. However, administration of SL prevented the activation of the PINK/Parkin pathway and inhibited excessive mitochondrial autophagy to regulate mitochondrial dysfunction. Results also demonstrated that mitochondrial dysfunction stimulated endothelial cell barrier dysfunction, but Evans blue transmission was significantly decreased and transmembrane resistance was increased significantly by SL treatment (p < 0.05 or p < 0.01). Carbonylcyanide‐3‐chlorophenylhydrazone (CCCP) could activate the PINK/Parkin pathway. CCCP reversed the regulation of SL on mitochondrial autophagy and mitochondrial function. SL could alleviate coronary artery no‐reflow by protecting the microvasculature by regulating mitochondrial function. The underlying mechanism was related to decreased mitochondrial autophagy by the PINK/Parkin pathway.
Lanthanide (such as Tb and Eu) metal–organic frameworks (MOFs) have been widely used in fluorescent probes because of their multiple coordination modes and brilliant fluorescence characteristic. Many ...lanthanide MOFs were applied in detecting metal ions, inorganic anions, and small molecules. However, it’s rarely reported that Ln-MOF was devoted to detecting malachite green (MG) and uric acid (UA). We prepared a europium-based metal–organic framework (Eu-TDA) (TDA = 2,5-thiophenedicarboxylic acid group). Luminescence studies demonstrated that Eu-TDA can rapidly detect MG and UA with excellent selectivity and sensitivity, where individual quenching efficiency K sv (MG: 5.8 × 105 M–1; UA: 4.15 × 104 M–1) and detection limit (MG: 0.0221 μM; UA: 0.689 μM) were regarded as the excellent MOF sensors for detecting MG and UA. The quenching of Eu-TDA’s fluorescence emission by MG and UA was likely due to the spectral overlap, energy transfer, and competition. Among 11 metal cations and 14 anions, Eu-TDA can quickly and effectively recognize MG and UA with highly selective and sensitive properties. Our method possesses potential application in detecting UA in human blood and MG in the fishpond.
Second-order topological superconductors host Majorana corner and hinge modes in contrast to conventional edge and surface modes in two and three dimensions. However, the realization of such ...second-order corner modes usually demands unconventional superconducting pairing or complicated junctions or layered structures. Here we show that Majorana corner modes could be realized using a 2D quantum spin Hall insulator in proximity contact with an s -wave superconductor and subject to an in-plane Zeeman field. Beyond a critical value, the in-plane Zeeman field induces opposite effective Dirac masses between adjacent boundaries, leading to one Majorana mode at each corner. A similar paradigm also applies to 3D topological insulators with the emergence of Majorana hinge states. Avoiding complex superconductor pairing and material structure, our scheme provides an experimentally realistic platform for implementing Majorana corner and hinge states.
Crystalline cluster materials, a class of functional motif aggregations, provide a great opportunity for tuning the properties stemming from the flexible and accurate variation of inorganic and ...organic compositions. In this study, we demonstrate the effects of functional ligand and ring size regulation on the structures and third‐order nonlinear optical (NLO) properties. Revealed by the single‐crystal X‐ray analysis results, aluminum molecular ring expansion is achieved by 2×9 and 3×6 strategies. In terms of the given organic shells, we further tuned the aluminum molecular ring sizes from 3.0 nm to 1.7 nm. The picosecond Z‐scan measurements results revealed that the third‐order NLO performances do not only depend on the general conjugate interactions but are also related to hydrogen bonding, polarizability, and ring sizes. The large nonlinear absorption coefficient and onset prove that the observed samples are promising candidates for the field of nonlinear optics.
A synthetic approach to generate the largest aluminum molecular rings is presented. Their nonlinear optics (NLO) and optical limiting (OL) performance is studied by the Z‐scan technique. The results provide insights to understand the NLO structure–activity relationship and tune the NLO performance at a molecular level.
Designing an architecture with the ability to temporarily capture one kind of charge carrier has a critical role to play in enhancing the performance of photocatalytic reactions. Here, we report that ...SrTiO3 nanofibers that have been treated with a brief method of H2 calcination in an H2/N2 atmosphere (denoted as STO-NH) form oxygen vacancies (OVs) and achieve significant improvement in performance in photocatalytic H2 production without the presence of cocatalysts. These OVs can trap photogenerated electrons, which inhibits the recombination of electrons and holes in both the surface and the bulk, thus improving the photocatalytic decomposition of water. Moreover, the concentration of surface OVs in STO-NH presents volcanic characteristics: the increase with rise in hydrogenation temperature, with a consequent increase in catalytic activity, indicates well-controlled formation of OVs. The existence and concentration of the OVs in STO-NH photocatalysts are investigated qualitatively through electron paramagnetic resonance, high-resolution transmission electron microscope and photoluminescence emission spectra. A reasonable photocatalytic mechanism is proposed that we expect to be able to provide significant guidance for future study.
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