Regulating the Topology of Covalent Organic Frameworks for Boosting Overall H2O2 Photogeneration.

Photocatalytic oxygen reduction reactions and water oxidation reactions are extremely promising green approaches for massive H2O2 production. Nonetheless, constructing effective photocatalysts for H2O2 generation is critical and still challenging. Since the network topology has significant impacts on the electronic properties of two dimensional (2D) polymers, herein, for the first time, we regulated the H2O2 photosynthetic activity of 2D covalent organic frameworks (COFs) by topology. Through designing the linking sites of the monomers, we synthesized a pair of novel COFs with similar chemical components on the backbones but distinct topologies. Without sacrificial agents, TBD-COF with cpt topology exhibited superior H2O2 photoproduction performance (6085 and 5448 µmol g-1 h-1 in O2 and air) than TBC-COF with hcb topology through the O2-O2⋅--H2O2, O2-O2⋅--O2 1-H2O2, and H2O-H2O2 three paths. Further experimental and theoretical investigations confirmed that during the H2O2 photosynthetic process, the charge carrier separation efficiency, O2⋅- generation and conversion, and the energy barrier of the rate determination steps in the three channels, related to the formation of *OOH, *O2 1, and *OH, can be well tuned by the topology of COFs. The current study enlightens the fabrication of high-performance photocatalysts for H2O2 production by topological structure modulation.

Mixed-Linkage Donor-Acceptor Covalent Organic Framework as a Turn-On Fluorescent Sensor for Aliphatic Amines.

Amine determination is crucial to our daily life, including the prevention of pollution, the treatment of certain disorders, and the evaluation of food quality. Herein, a mixed-linkage donor-acceptor covalent organic framework (named DSE-COF) was first constructed by the polymerization between 2,4-dihydroxybenzene-1,3,5-tricarbaldehyde (DTA) and 4,4'-(benzo[c][1,2,5]selenadiazole-4,7-diyl)dianiline (SEZ). DSE-COF displayed superior turn-on fluorescent responses to primary, secondary, and tertiary aliphatic amines, such as cadaverine, isopropylamine, sec-butylamine, cyclohexylamine, hexamethylenediamine, di-n-butylamine, and triethylamine in absolute acetonitrile than other organic species. Further experiments and theoretical calculations demonstrated that the combination of intramolecular charge transfer (ICT) and photoinduced electron transfer (PET) effects between the DSE-COF and aliphatic amines resulted in enhanced fluorescence. Credibly, DSE-COF can quantitatively detect cadaverine content in actual pork samples with satisfactory results. In addition, DSE-COF-based test papers could rapidly monitor cadaverine from real pork samples, manifesting the potential application of COFs in food quality inspection.

Thiophene-Containing Covalent Organic Frameworks for Overall Photocatalytic H2 O2 Synthesis in Water and Seawater.

H2 O2 is a significant chemical widely utilized in the environmental and industrial fields, with growing global demand. Without sacrificial agents, simultaneous photocatalyzed H2 O2 synthesis through the oxygen reduction reaction (ORR) and water oxidation reaction (WOR) dual channels from seawater is green and sustainable but still challenging. Herein, two novel thiophene-containing covalent organic frameworks (TD-COF and TT-COF) were first constructed and served as catalysts for H2 O2 synthesis via indirect 2e- ORR and direct 2e- WOR channels. The photocatalytic H2 O2 production performance can be regulated by adjusting the N-heterocycle modules (pyridine and triazine) in COFs. Notably, with no sacrificial agents, just using air and water as raw materials, TD-COF exhibited high H2 O2 production yields of 4060 µmol h-1 g-1 and 3364 µmol h-1 g-1 in deionized water and natural seawater, respectively. Further computational mechanism studies revealed that the thiophene was the primary photoreduction unit for ORR, while the benzene ring (linked to the thiophene by the imine bond) was the central photooxidation unit for WOR. The current work exploits thiophene-containing COFs for overall photocatalytic H2 O2 synthesis via ORR and WOR dual channels and provides fresh insight into creating innovative catalysts for photocatalyzing H2 O2 synthesis.

Chiral Ionic Covalent Organic Framework as an Enantioselective Fluorescent Sensor for Phenylalaninol Determination.

Phenylalaninol (PAL) is a significant chemical intermediate widely utilized in drug development and chiral synthesis, for instance, as a reactant for bicyclic lactams and oxazoloisoindolinones. Since the absolute stereochemical configuration significantly impacts biological action, it is crucial to evaluate the concentration and enantiomeric content of PAL in a quick and convenient manner. Herein, an effective PAL enantiomer recognition method was reported based on a chiral ionic covalent organic framework (COF) fluorescent sensor, which was fabricated via one-step postquaternization modification of an achiral COF by (1R, 2S, 5R)-2-isopropyl-5-methylcyclohexyl-carbonochloridate (L-MTE). The formed chiral L-TB-COF can be applied as a chiral fluorescent sensor to recognize the stereochemical configuration of PAL, which displayed a turn-on fluorescent response for R-PAL over that of S-PAL with an enantioselectivity factor of 16.96. Nonetheless, the single L-MTE molecule had no chiral recognition ability for PAL. Moreover, the ee value of PAL can be identified by L-TB-COF. Furthermore, density functional theory (DFT) calculations demonstrated that the chiral selectivity came from the stronger binding affinity between L-TB-COF and R-PAL in comparison to that with S-PAL. L-TB-COF is the first chiral ionic COF employed to identify chiral isomers by fluorescence. The current work expands the range of applications for ionic COFs and offers fresh suggestions for creating novel chiral fluorescent sensors.

Silencing of the calcium-dependent protein kinase TaCDPK27 improves wheat resistance to powdery mildew.

BACKGROUND: Calcium ions (Ca2+), secondary messengers, are crucial for the signal transduction process of the interaction between plants and pathogens. Ca2+ signaling also regulates autophagy. As plant calcium signal-decoding proteins, calcium-dependent protein kinases (CDPKs) have been found to be involved in biotic and abiotic stress responses. However, information on their functions in response to powdery mildew attack in wheat crops is limited. RESULT: In the present study, the expression levels of TaCDPK27, four essential autophagy-related genes (ATGs) (TaATG5, TaATG7, TaATG8, and TaATG10), and two major metacaspase genes, namely, TaMCA1 and TaMCA9, were increased by powdery mildew (Blumeria graminis f. sp. tritici, Bgt) infection in wheat seedling leaves. Silencing TaCDPK27 improves wheat seedling resistance to powdery mildew, with fewer Bgt hyphae occurring on TaCDPK27-silenced wheat seedling leaves than on normal seedlings. In wheat seedling leaves under powdery mildew infection, silencing TaCDPK27 induced excess contents of reactive oxygen species (ROS); decreased the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT); and led to an increase in programmed cell death (PCD). Silencing TaCDPK27 also inhibited autophagy in wheat seedling leaves, and silencing TaATG7 also enhanced wheat seedling resistance to powdery mildew infection. TaCDPK27-mCherry and GFP-TaATG8h colocalized in wheat protoplasts. Overexpressed TaCDPK27-mCherry fusions required enhanced autophagy activity in wheat protoplast under carbon starvation. CONCLUSION: These results suggested that TaCDPK27 negatively regulates wheat resistance to PW infection, and functionally links with autophagy in wheat.

Fluorescence/Colorimetry/Smartphone Triple-Mode Sensing of Dopamine by a COF-Based Peroxidase-Mimic Platform.

Simple and accurate monitoring of urinary dopamine (DA) concentration is significant, which is helpful for the assessment or exclusion of catecholamine-producing tumors, such as pheochromocytoma and paraganglioma. Herein, a fluorescence/colorimetry/smartphone triple-mode sensing platform for DA determination was constructed using copper ion (Cu2+)-modified hydrazone-linked covalent organic frameworks (Cu-BTA-COF). Cu-BTA-COF with 21.67 wt % copper content exhibited peroxidase-mimic activity. After adding H2O2 and 1,3-dihydroxynaphthalene, the Cu-BTA-COF platform can sensitively and selectively detect DA in three modes with consistent results. In fluorescence/colorimetry/smartphone modes, the linear ranges of DA were 1-10, 0.2-40, and 1-10 µM, with related detection limits of 7.2, 8.6, and 23 nM, respectively. Moreover, the Cu-BTA-COF platform can be explored for DA determination in human urine samples with satisfactory recoveries (97.6-100.4%) in all the three modes, suggesting the potential practical application of the Cu-BTA-COF platform for DA detection in urine.

The Calcium-Dependent Protein Kinase TaCDPK27 Positively Regulates Salt Tolerance in Wheat.

As essential calcium ion (Ca2+) sensors in plants, calcium-dependent protein kinases (CDPKs) function in regulating the environmental adaptation of plants. However, the response mechanism of CDPKs to salt stress is not well understood. In the current study, the wheat salt-responsive gene TaCDPK27 was identified. The open reading frame (ORF) of TaCDPK27 was 1875 bp, coding 624 amino acids. The predicted molecular weight and isoelectric point were 68.905 kDa and 5.6, respectively. TaCDPK27 has the closest relationship with subgroup III members of the CDPK family of rice. Increased expression of TaCDPK27 in wheat seedling roots and leaves was triggered by 150 mM NaCl treatment. TaCDPK27 was mainly located in the cytoplasm. After NaCl treatment, some of this protein was transferred to the membrane. The inhibitory effect of TaCDPK27 silencing on the growth of wheat seedlings was slight. After exposure to 150 mM NaCl for 6 days, the NaCl stress tolerance of TaCDPK27-silenced wheat seedlings was reduced, with shorter lengths of both roots and leaves compared with those of the control seedlings. Moreover, silencing of TaCDPK27 further promoted the generation of reactive oxygen species (ROS); reduced the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT); aggravated the injury to photosystem II (PS II); and increased programmed cell death (PCD) in wheat leaves under NaCl treatment, confirming that the TaCDPK27-silenced seedlings exhibited more NaCl injury than control seedlings. Taken together, the decrease in NaCl tolerance in TaCDPK27-silenced seedlings was due to excessive ROS accumulation and subsequent aggravation of the NaCl-induced PCD. TaCDPK27 may be essential for positively regulating salt tolerance in wheat seedlings.

The Metacaspase TaMCA-Id Negatively Regulates Salt-Induced Programmed Cell Death and Functionally Links With Autophagy in Wheat.

Metacaspases (MCAs), a family of caspase-like proteins, are important regulators of programmed cell death (PCD) in plant defense response. Autophagy is an important regulator of PCD. This study explored the underlying mechanism of the interaction among PCD, MCAs, and autophagy and their impact on wheat response to salt stress. In this study, the wheat salt-responsive gene TaMCA-Id was identified. The open reading frame (ORF) of TaMCA-Id was 1,071 bp, coding 356 amino acids. The predicted molecular weight and isoelectric point were 38,337.03 Da and 8.45, respectively. TaMCA-Id had classic characteristics of type I MCAs domains, a typical N-terminal pro-domain rich in proline. TaMCA-Id was mainly localized in the chloroplast and exhibited nucleocytoplasmictrafficking under NaCl treatment. Increased expression of TaMCA-Id in wheat seedling roots and leaves was triggered by 150 mM NaCl treatment. Silencing of TaMCA-Id enhanced sensitivity of wheat seedlings to NaCl stress. Under NaCl stress, TaMCA-Id-silenced seedlings exhibited a reduction in activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), higher accumulation of H2O2 and O 2 . - , more serious injury to photosystem II (PSII), increase in PCD level, and autophagy activity in leaves of wheat seedlings. These results indicated that TaMCA-Id functioned in PCD through interacting with autophagy under NaCl stress, which could be used to improve the salt tolerance of crop plants.

Ratiometric Fluorescent pH Sensor Based on a Tunable Multivariate Covalent Organic Framework.

Ratiometric detection of pH is always significant in environmental regulation, medical diagnosis, synthetic chemistry, and beyond. The construction of practical ratiometric pH sensors with reusability is still challenging. Herein, by exploiting a multivariate strategy, we first synthesized and reported a series of novel three-component covalent organic frameworks (COF-COOHX, X = 33, 50, and 67) through Schiff base reaction between 2-hydroxybenzene-1,3,5-tricarbaldehyde (HTA), 4,4'-diamino-3,3'-biphenyldicarboxylic acid (DBA), and 5,5'-diamino-2,2'-bipyridine (BPY) at various molar ratios (X = [DBA]/([BPY] + [DBA]) × 100 = 33, 50, and 67). COF-COOHX (X = 33, 50, and 67) displayed ratiometric pH sensing performance in acidic conditions with selectivity and repeatability. By tuning the molar ratio of DBA and BPY, the fluorescent properties, linear pH responsive ranges, and pKa values of COF-COOHX (X = 33, 50, and 67) can be regulated. Meanwhile, the two-component COF-COOH0 and COF-COOH100 did not exhibit ratiometric pH detection ability. Moreover, the constructed three ratiometric sensors can be applied to detect pH in drug solutions and carbonated drinks with satisfactory results. This work sheds new light on the design and fabrication of innovative ratiometric fluorescent sensors using COFs.

Two-dimensional porphyrin covalent organic frameworks with tunable catalytic active sites for the oxygen reduction reaction.

Four novel two-dimensional porphyrin COFs (M-TP-COF, M = H2, Co, Ni and Mn) with donor-acceptor dyads were fabricated and served as electrocatalysts for the oxygen reduction reaction (ORR). The ORR catalytic activity of M-TP-COF was tuned by changing the M atom in the center of the porphyrin backbone. The experimental structure-function relationship was in accordance with the results of density functional theory calculations based on the O2-O2*-OOH*-O*-OH*-OH- route.

Silencing of ATG2 and ATG7 promotes programmed cell death in wheat via inhibition of autophagy under salt stress.

Salt stress, as an abiotic stress, limits crops production worldwide. Autophagy and programmed cell death (PCD) have been functionally linked to plant adaptation to abiotic stress. However, the relation of autophagy and PCD is still under debate and the mechanism behind remains not fully understood. In this study, salt-tolerant wheat cultivar Jimai22 was used as the experimental material, and 150 mM NaCl was added to the hydroponic culture to test the effect of salt treatment. The results showed that NaCl stress enhances autophagic activity and induced occurrence of PCD in roots and leaves of wheat seedlings. Then, the barley stripe mosaic virus-induced silencing (BSMV-VIGS) method was used to inhibit autophagy by silencing the expression of ATG2 or ATG7. The results showed that silencing of ATG2 or ATG7 significantly inhibited autophagy and impaired the tolerance of wheat to NaCl stress. Moreover, silencing of ATG2 or ATG7 disrupted the absorption of Na, Cl, K and Ca elements and led to subsequent disequilibrium of Na+, Cl-, K+ and Ca2+, induced generation of excess reactive oxygen species (ROS), decreased the antioxidant activity, damaged photosynthesis apparatus, increased the level of PCD and led to differential expression of the genes, two metacaspase genes, cysteine-rich receptor-like kinase (CRK) 10, and CRK26 in leaves of wheat seedlings under NaCl stress. The effect of the inhibitor 3-methyladenine (3-MA) on roots and leaves of wheat seedlings was in accordance with that of ATG2 and ATG7 silencing. Our results suggest that autophagy negatively regulates salt-induced PCD, or limits the scale of salt-induced PCD to avoid severe tissue death in wheat seedlings.

Linker-Eliminated Nano Metal-Organic Framework Fluorescent Probe for Highly Selective and Sensitive Phosphate Ratiometric Detection in Water and Body Fluids.

Phosphate is an important anion in both the aquatic environment and biological systems. The search for a selective and sensitive phosphate ratiometric fluorescent probe to quantify the phosphate level in water samples and body fluids is of great significance for the protection of the ecological environment and human health. Here, a porphyrin-based nano metal-organic framework (NMOF), PCN-224, was successfully exploited as a simple but highly sensitive and selective single-component ratiometric fluorescent probe with accurate composition and measurable structure for the quantitative determination of phosphate, based on the interesting double-emission fluorescence of the porphyrin ligand itself. Compared with other zirconium-based NMOF probes for phosphate, the reduced number of connections for ZrO clusters with the ligand in PCN-224 obtained by a linker-elimination strategy simultaneously provides more active recognition sites for phosphate, which effectively improves the sensitivity of the zirconium-based NMOF probes. The detection limit of the probe is only 54 nM. Additionally, the accuracy of the ratiometric detection based on this probe was further proved by the detection of phosphate in human serum and drinking water.

Metal ion-assisted carboxyl-containing covalent organic frameworks for the efficient removal of Congo red.

Covalent organic frameworks (COFs) have been utilized as molecular sieves to adsorb or remove or separate a wide range of substances. Herein, a new carboxyl-containing COF (COF-COOH) is fabricated from the polymerization of 1,3,5-triformylphloroglucinol (TP) and 4,4'-diamino-[1,1'-biphenyl]-3,3'-dicarboxylic acid (DBA). COF-COOH displays good adsorption performance on Congo red (CR) through hydrogen bonds and π-π stacking interactions. Through post-modification with Ca2+/Ni2+ ions, the adsorption capacity of COF-COOCa/COF-COONi to CR is improved, which is due to the coordinated metal cations having a positive contribution to the electrostatic interactions. At 25 °C, the maximum adsorption amount of COF-COOCa and COF-COONi to CR is 704.23 mg g-1 and 781.25 mg g-1, respectively. The removal efficiency of COF-COOCa to CR is 95% and that of COF-COONi is 96%. This demonstrates that the new metal ion-assisted COFs are viable adsorbents to remove dye pollutants, which are harmful to the environment and to human health, from wastewater.

Insight into the Transimination Process in the Fabrication of Surface Schiff-Based Covalent Organic Frameworks.

The on-surface synthesis of single-layered covalent organic frameworks (sCOFs) has been investigated by employing a 3-fold symmetric monomer 1 carrying aldehyde groups and the ditopic diamine building block 2 on a highly oriented pyrolytic graphite surface. The self-assembly of molecule 1 is persistently observed at the stoichiometric ratio of the reactive groups. The growth of sCOF network is observed, however, only at the excess of diamine monomers. By investigating the growth process of the sCOF network, the role of excessive diamine monomers can be understood by two aspects. Increasing the molar ratio of diamine monomer provides the driving force for the structural transition from the monomer self-assembly to the formation of the sCOF network. On the other hand, the excess diamine monomers provide basic environment for the transimination reaction and promote the formation of highly ordered sCOFs. The present work provides molecular understanding of the role of transimination reaction in imine-based COF synthesis.

Switching the surface homochiral assembly by surface host-guest chemistry.

We combine chiral amplification and host-guest chemistry to demonstrate an approach to achieve a switchable chiral assembly. After the addition of the guest coronene, homochiral honeycomb patterns transform into host-guest sunflower structures, in which supramolecular chirality is modulated dramatically.

Simultaneous construction of two linkages for the on-surface synthesis of imine-boroxine hybrid covalent organic frameworks.

The orthogonality between the Schiff base reaction and the boronic acid dehydration reaction is explored during the on-surface synthesis process. By activating the above two reactions in one-step and employing asymmetrical substituted monomers and the 3-fold symmetric monomer 1,3,5-tris(4-aminophenyl)benzene (TAPB), highly ordered imine-boroxine hybrid single-layered covalent organic frameworks (sCOFs) have been successfully constructed on HOPG by a gas-solid interface reaction method and characterized by scanning tunnelling microscopy (STM). In particular, the reaction between the meta-substituted monomer and TAPB generates sCOFB with a windmill structure, which is the first sCOF with surface chirality so far reported. The demonstration of the one-step synthesis of multiple linkages to form sCOFs can further enlarge the sCOF family and expand the design routes for functional 2D organic nanomaterials.

Construction of 2D nanoporous networks by coupling on-surface dynamic imine chemistry and dipole-stabilized self-assembly.

Double-walled nanoporous networks based on the Schiff base reaction of nonplanar tripodic building blocks and subsequent dipole-directed self-assembly were fabricated on highly oriented pyrolytic graphite (HOPG) at the gas-solid interface. This is the first example of nonplanar molecules exploited as precursors for a surface reaction.

Manifesting the sergeants-and-soldiers principle in coadsorber induced homochiral polymorphic assemblies at the liquid/solid interface.

We systematically studied the operation of coadsorber-induced surface chirality in a series of enantiomeric surface supramolecular assemblies. The correlation of chiral amplification degree with the proportion of enantiomeric interaction in the total intermolecular interaction is deduced.

Fabrication of bilayer tetrathiafulvalene integrated surface covalent organic frameworks.

A bilayer covalent organic framework (COF) of TTF-based building blocks was obtained by imine reaction between tetrathiafulvalene tetraaldehyde (4ATTF) and p-phenylenediamine (PPDA). Direct evidence for the eclipsed stacking of bilayer structure via π-π interaction between TTF units is provided by high resolution scanning tunneling microscopy.

The on-surface synthesis of imine-based covalent organic frameworks with non-aromatic linkage.

A pair of isomeric imine-based covalent organic frameworks with non-aromatic linkage has been fabricated at the graphite surface, which extends the structural diversity of surface covalent organic frameworks.