Self-assembled mononuclear complexes: open metal sites and inverse dimension-dependent catalytic activity for the Knoevenagel condensation and CO2 cycloaddition.

To lessen the greenhouse effect, measures such as improving the recovery of crude oil and converting carbon dioxide (CO2) into valuable chemicals are necessary to create a sustainable low-carbon future. To this end, the development of efficient new oil-displacing agents and CO2 conversion has aroused great interest in both academia and industry. The Knoevenagel condensation and CO2 cycloaddition are the key reactions to solve the above problems. Four Cu- or Zn-based molecular complexes built from different ligands possessing hydrophilic-hydrophobic layers and different dimensionalities were chosen as solid catalysts for this study. Structural analysis revealed the presence of hydrophilic-hydrophobic layers and open metal sites in the low-dimensional complexes. To obtain deep insight into the reaction mechanism, first-principles density functional theory (DFT) calculations were carried out. These calculations confirmed that in the Knoevenagel condensation reaction, the final formation of benzylidenemalononitrile is the rate-determining step (an energy barrier (ΔE) value of 73.2 kJ mol-1). The zero-dimensional (0D) Cu molecular complex with unsaturated metal centers, hydrophilic and hydrophobic layers, exhibited higher catalytic activity (yield: 100%, temperature: room temperature, and time: 2 h) compared with one- and two-dimensional Cu complexes. In the presence of a 0D Zn complex co-catalyzed with Br- in the CO2 cycloaddition reaction, the ΔE value reduces to 35.5 kJ mol-1 for the ring opening of styrene oxide (SO), which is significantly lower than Br- catalyzed (80.9 kJ mol-1) reactions. The roles of unsaturated metal centers, hydrophilic-hydrophobic layers and dimensionality in the Knoevenagel condensation and CO2 cycloaddition were explained in the results of structure-activity relationships.

Strong Electronic Metal-Support Interaction between Iridium Single Atoms and a WO3 Support Promotes Highly Efficient and Robust CO2 Cycloaddition.

The carbon dioxide (CO2 ) cycloaddition of epoxides to cyclic carbonates is of great industrial importance owing to the high economical values of its products. Single-atom catalysts (SACs) have great potential in CO2 cycloaddition by virtue of their high atom utilization efficiency and desired activity, but they generally suffer from poor reaction stability and catalytic activity arising from the weak interaction between the active centers and the supports. In this work, Ir single atoms stably anchored on the WO3 support (Ir1 -WO3 ) are developed with a strong electronic metal-support interaction (EMSI). Superior CO2 cycloaddition is realized in the Ir1 -WO3 catalyst via the EMSI effect: 100% conversion efficiency for the CO2 cycloaddition of styrene oxide to styrene carbonate after 15 h at 40 °C and excellent stability with no degradation even after ten reaction cycles for a total of more than 150 h. Density functional theory calculations reveal that the EMSI effect results in significant charge redistribution between the Ir single atoms and the WO3 support, and consequently lowers the energy barrier associated with epoxide ring opening. This work furnishes new insights into the catalytic mechanism of CO2 cycloaddition and would guide the design of stable SACs for efficient CO2 cycloaddition reactions.

Single-ion chelation strategy for synthesis of monodisperse Pd nanoparticles anchored in MOF-808 for highly efficient hydrogenation and cascade reactions.

Ultrafine Pd nanoparticles are prepared using a single-ion precursor on a MOF-808 carrier. The ligand 2,3-pyrazinedicarboxylic acid (Pza) is dispersed in porous MOF-808 via grafting on formic acid sites, and thus Pd2+ ions are chelated by Pza to form a new single-ion precursor Pd@MOF-808-Pza. Then a Pd-nano@MOF-808-Pza catalyst is prepared by direct reduction of this precursor using NaBH4. Material characterization reveals the homogeneous dispersion of 3-6 nm Pd nanoparticles within the MOF-808 matrix. Pd-nano@MOF-808-Pza exhibits excellent catalytic activity in the hydrogenation of unsaturated nitrogen-containing compounds, and other typical reactions, such as the Knoevenagel condensation, Suzuki/Heck cross-coupling, and hydrogen tandem reactions. In addition, density functional theory (DFT) calculations are carried out to elucidate the chelation of Pd2+ ions by Pza on MOF-808 and propose mechanisms of hydrogenation reactions. This work provides an effective reduction catalyst, and more importantly, a single-ion chelation strategy for design and synthesis of metal supported catalysts.

Solvo-thermal synthesis of a unique cluster-based nano-porous zinc(II) luminescent metal-organic framework for highly sensitive detection of anthrax biomarker and dichromate.

In this work a flexible multi-dentate 4,4'-(1H-1,2,4-triazole-1-yl) methylene-bis(benzonic acid) (H2L) ligand has been employed, a unique cluster-based nano-porous luminescent zinc(II) metal-organic framework {[Zn(µ6-L)]·(DMAC)2}n (1) (DMAC = Dimethylacetamide) has been isolated under solvo-thermal conditions. The H2L ligand adopts hexa-dentate coordination modes via one triazole nitrogen atom and four aromatic carboxylate oxygen atoms, which bridge the neighboring six-coordinated ZnII centers, leading to a three-dimensional (3D) nano-porous metal organic framework. A PLATON program analysis suggests the total potential solvent area volume is 2028.9 Å3, which occupy 62.5% percent of the unit cell volume (3248.4 Å3). PXRD Patterns of the as-synthesized samples 1 have been determined confirming the purity of the bulky samples. Photo-luminescent properties indicate strong fluorescent emissions of 1 at the room temperature. Further photo-luminescent measurements show that 1 can exhibit highly sensitive real-time luminescence sensing of anthrax biomarker dipicolinic acid (DPA) with high quenching efficiency (KSV = 1.48 × 105 M-1) and low detection limit (0.298 µM (S/N = 3)). Meanwhile 1 also exhibits highly selective and sensitive luminescence sensing for Cr2O72- ions in aqueous solutions with high quenching efficiency KSV = 1.22 × 104 L·mol-1 and low detection limit (0.023 µM (S/N = 3)). Therefore 1 can be used a unique multi-functional 3D cluster-based metal organic material in sensitive detection and effective detection of environment pollutants and biomarker molecules.

Nitrogen-Deficient Graphitic Carbon Nitride with Enhanced Performance for Lithium Ion Battery Anodes.

Graphitic carbon nitride (g-C3N4) behaving as a layered feature with graphite was indexed as a high-content nitrogen-doping carbon material, attracting increasing attention for application in energy storage devices. However, poor conductivity and resulting serious irreversible capacity loss were pronounced for g-C3N4 material due to its high nitrogen content. In this work, magnesiothermic denitriding technology is demonstrated to reduce the nitrogen content of g-C3N4 (especially graphitic nitrogen) for enhanced lithium storage properties as lithium ion battery anodes. The obtained nitrogen-deficient g-C3N4 (ND-g-C3N4) exhibits a thinner and more porous structure composed of an abundance of relatively low nitrogen doping wrinkled graphene nanosheets. A highly reversible lithium storage capacity of 2753 mAh/g was obtained after the 300th cycle with an enhanced cycling stability and rate capability. The presented nitrogen-deficient g-C3N4 with outstanding electrochemical performances may unambiguously promote the application of g-C3N4 materials in energy-storage devices.

Cyclic helix B peptide protects HK­2 cells from oxidative stress by inhibiting ER stress and activating Nrf2 signalling and autophagy.

Renal ischemia­reperfusion injury (IRI) is present in numerous diseases and is observed following certain treatments, including renal transplantation. Preventing tubular epithelial cells (TECs) from undergoing apoptosis is vital for treatment of renal IRI. Cyclic helix B peptide (CHBP) is a novel agent that has a protective effect on renal IRI in vivo. In the present study, the effect and underlying mechanism of CHBP on TECs was investigated. The HK­2 human renal proximal tubular epithelial cell line was treated with 500 µmol/l H2O2 for 4 h prior to determining the effect of CHBP pretreatment for 1 h on cell viability, caspase 3 activity and expression levels, expression levels of oxidative stress markers, endoplasmic reticulum (ER) stress markers, NF­E2­related factor 2 (Nrf2), heme oxygenase­1 (HO­1) and autophagy markers. This was investigated using a Cell Counting kit 8, a terminal deoxynucleotidyl transferase­mediated dUTP nick­end labelling assay, western blotting, reverse transcription­quantitative polymerase chain reaction and immunocytochemistry. Results revealed that pretreatment with CHBP enhanced HK­2 cell viability, the glutathione/glutathione disulphide ratio, activation of Nrf2 and mRNA expression levels of HO­1 and the expression levels of beclin­1 and light chain 3 A/B­II/I. Conversely, CHBP pretreatment reduced the expression levels of reactive oxygen species, the activity and protein expression levels of capase­3, the mRNA and protein expression levels of C/EBP homologous protein and binding immunoglobulin protein, and the expression levels of phosphorylated (p)­mechanistic target of rapamycin (mTOR) Ser2448 and p62 during oxidative stress. However, the expression of p­mTOR Ser2481 was enhanced after CHBP pretreatment. CHBP pretreatment reduced the expression levels of reactive oxygen species, the activity and protein expression levels of capase­3, the mRNA and protein expression levels of C/EBP homologous protein and binding immunoglobulin protein, and the expression levels of phosphorylated (p)­mechanistic target of rapamycin (mTOR) Ser2481, p62 and p­mTOR Ser 2448 during oxidative stress. In conclusion, CHBP pretreatment protected HK­2 cells from H2O2­induced injury, inhibited ER stress and pro­apoptotic pathways, and activated the Nrf2 signalling pathway and autophagy. These results provide a potential mechanism of how CHBP protects against renal IRI.

Intramolecular hydrogen bonds quench photoluminescence and enhance photocatalytic activity of carbon nanodots.

Understanding the photoluminescence (PL) and photocatalytic properties of carbon nanodots (CNDs) induced by environmental factors such as pH through surface groups is significantly important to rationally tune the emission and photodriven catalysis of CNDs. Through adjusting the pH of an aqueous solution of CNDs, it was found that the PL of CNDs prepared by ultrasonic treatment of glucose is strongly quenched at pH 1 because of the formation of intramolecular hydrogen bonds among the oxygen-containing surface groups. The position of the strongest PL peak and its corresponding excitation wavelength strongly depend on the surface groups. The origins of the blue and green emissions of CNDs are closely related to the carboxyl and hydroxyl groups, respectively. The deprotonated COO(-) and CO(-) groups weaken the PL peak of the CNDs and shift it to the red. CNDs alone exhibit photocatalytic activity towards degradation of Rhodamine B at different pH values under UV irradiation. The photocatalytic activity of the CNDs is the highest at pH 1 because of the strong intramolecular hydrogen bonds formed among the oxygen-containing groups.

Rapamycin protects kidney against ischemia reperfusion injury through recruitment of NKT cells.

BACKGROUND: NKT cells play a protective role in ischemia reperfusion (IR) injury, of which the trafficking in the body and recruitment in injured organs can be influenced by immunosuppressive therapy. Therefore, we investigated the effects of rapamycin on kidneys exposed to IR injury in early stage and on trafficking of NKT cells in a murine model. MATERIAL AND METHODS: Balb/c mice were subjected to kidney 30 min ischemia followed by 24 h reperfusion. Rapamycin (2.5 ml/kg) was administered by gavage daily, starting 1 day before the operation. Renal function and histological changes were assessed. The proportion of NKT cells in peripheral blood, spleen and kidney was detected by flow cytometry. The chemokines and corresponding receptor involved in NKT cell trafficking were determined by RT-PCR and flow cytometry respectively. RESULTS: Rapamycin significantly improved renal function and ameliorated histological injury. In rapamycin-treated group, the proportion of NKT cells in spleen was significantly decreased but increased in peripheral blood and kidney. In addition, the CXCR3+ NKT cell in the kidney increased remarkably in the rapamycin-treated group. The chemokines, CXCL9 and CXCL10, as the ligands of CXCR3, were also increased in the rapamycin-treated kidney. CONCLUSIONS: Rapamycin may recruit NKT cells from spleen to the IR-induced kidney to ameliorate renal IR injury in the early stage.