17 research outputs found

    Controlled Ring-Opening of Siloxy­difluoro­cyclo­propanes for Carbocyclization: Synthesis of Difluoro­cyclo­pentenones

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    A highly controlled ring opening of siloxy­difluoro­cyclo­propanes, formed by <i>n</i>BuN<sub>4</sub>Br-catalyzed difluorocyclo­propanation of methyl vinyl ketones bearing a β-alkylthio group by using TMSCF<sub>2</sub>Br as a unique difluorocarbene source, results in metal difluoro­homoenolates with assistance of copper or silver followed by an intramolecular addition and elimination reaction leading to α-<i>gem</i>-difluorocyclopentenones efficiently

    Ring-Opening Diarylation of Siloxydifluorocyclopropanes by Ag(I) Catalysis: Stereoselective Construction of 2‑Fluoroallylic Scaffold

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    A silver-catalyzed, defluorination ring-opening diarylation of siloxy 2,2-difluorocyclopropanes, with two arenes, to directly prepare polysubstituted 2-fluoroallylic compounds, is described. This multicomponent reaction proceeds smoothly in good stereoselectivity, which is due to a chelation-controlled addition of arenes to α-fluorinated ketone intermediate

    Lateral-Size-Mediated Efficient Oxygen Evolution Reaction: Insights into the Atomically Thin Quantum Dot Structure of NiFe<sub>2</sub>O<sub>4</sub>

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    The study of high-performance electrocatalysts for driving the oxygen evolution reaction (OER) is important for energy storage and conversion systems. As a representative of inverse-spinel-structured oxide catalysts, nickel ferrite (NiFe<sub>2</sub>O<sub>4</sub>) has recently gained interest because of its earth abundance and environmental friendliness. However, the gained electrocatalytic performance of NiFe<sub>2</sub>O<sub>4</sub> for the OER is still far from the state-of-the-art requirements because of its poor reactivity and finite number of surface active sites. Here, we prepared a series of atomically thin NiFe<sub>2</sub>O<sub>4</sub> catalysts with different lateral sizes through a mild and controllable method. We found that the atomically thin NiFe<sub>2</sub>O<sub>4</sub> quantum dots (AT NiFe<sub>2</sub>O<sub>4</sub> QDs) show the highest OER performance with a current density of 10 mA cm<sup>–2</sup> at a low overpotential of 262 mV and a small Tafel slope of 37 mV decade<sup>–1</sup>. The outstanding OER performance of AT NiFe<sub>2</sub>O<sub>4</sub> QDs is even comparable to that of commercial RuO<sub>2</sub> catalyst, which can be attributed to its high reactivity and the high fraction of active edge sites resulting from the synergetic effect between the atomically thin thickness and the small lateral size of the atomically thin quantum dot (AT QD) structural motif. The experimental results reveal a negative correlation between lateral size and OER performance in alkaline media. Specifically speaking, the number of low-coordinated oxygen atoms increases with decreasing lateral size, and this leads to significantly more oxygen vacancies that can lower the adsorption energy of H<sub>2</sub>O, increasing the catalytic OER efficiency of AT NiFe<sub>2</sub>O<sub>4</sub> QDs

    Comparative Study of Homogeneous and Heterogeneous Photocatalytic Degradation of RhB under Visible Light Irradiation with Keggin-Type Manganese-Substituted Catalysts

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    This paper reported for the first time a comparative study of the photocatalytic activity of the Keggin-type Mn­(II)-substituted heteropolyanion PW<sub>11</sub>O<sub>39</sub>Mn<sup>II</sup>(H<sub>2</sub>O)<sup>5–</sup> (PW<sub>11</sub>Mn) and its heterogeneous system PW<sub>11</sub>Mn/D301R through the degradation of rhodamine B (RhB) under visible light irradiation. A novel photocatalytic mechanism was suggested, and an interaction between PW<sub>11</sub>Mn and RhB was scrutinized by using visible absorption spectrum and fluorescence emission spectrum. Influences of some factors such as the RhB initial concentration, the PW<sub>11</sub>Mn concentration, the PW<sub>11</sub>Mn/D301R dosage, the solution pH, and different anions existing in solution on the photocatalytic degradation rate of RhB were also examined. The stability of PW<sub>11</sub>Mn/D301R was evaluated by the cycle photodegradation of RhB in the end. The experimental results showed that 100% of RhB degradation was reached at 100 min for the PW<sub>11</sub>Mn system and 40 min for the PW<sub>11</sub>Mn/D301R system when the solution containing 10 μmol·L<sup>–1</sup>RhB was exposed to visible light. The hydroxyl radicals were responsible for the destruction of dye. The photocatalysis mechanism was different from that of both semiconductor and Keggin parent catalysts. An electrostatic interaction and a coordination interaction between PW<sub>11</sub>Mn and RhB occurred simultaneously in an acidic aqueous solution. The coordination interaction slowed significantly the RhB degradation, but became weak obviously after PW<sub>11</sub>Mn was adsorbed onto the D301R resin. The influence of anions existing in solution on the RhB degradation followed the sequence of PO<sub>4</sub><sup>3–</sup> > SO<sub>4</sub><sup>2–</sup>> Cl<sup>–</sup>> NO<sub>3</sub><sup>–</sup>. No matter if in neutral or in acidic aqueous solution, the photocatalyst PW<sub>11</sub>Mn/D301R was stable

    Bipoladien A, a Sesterterpenoid Containing an Undescribed 5/8/5/7 Carbon Skeleton from Bipolaris maydis

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    Bipoladiens A–E (1–5), five new ophiobolin-derived sesterterpenoids, and a known compound 6 (bipolaricin R) were isolated from the cultures of the phytopathogenic fungus Bipolaris maydis. Their structures and absolute configurations were elucidated based on comprehensive spectroscopic analyses, HRESIMS, electronic circular dichroism (ECD) calculations, and single-crystal X-ray diffraction analyses. Notably, compound 1 has an undescribed tetracyclic 5/8/5/7 fused carbon skeleton, and compound 2 possesses a rare multicyclic caged ring system. The biosynthetic pathway of 1 was proposed starting from 6 via a series of oxidation and cyclization reactions. Compound 6 showed excellent antiproliferation and apoptosis induction effects against A549 cell line. Additionally, compounds 5 and 6 exhibited noticeable antimicrobial ability against Bacillus cereus, Staphylococcus aureus, and Staphylococcus epidermidis. These findings not only developed the chemical and bioactivities diversities of ophiobolin-sesterterpenoid but also provided an idea to boost the application of natural products in the control of food pathogens

    Bipoladien A, a Sesterterpenoid Containing an Undescribed 5/8/5/7 Carbon Skeleton from Bipolaris maydis

    No full text
    Bipoladiens A–E (1–5), five new ophiobolin-derived sesterterpenoids, and a known compound 6 (bipolaricin R) were isolated from the cultures of the phytopathogenic fungus Bipolaris maydis. Their structures and absolute configurations were elucidated based on comprehensive spectroscopic analyses, HRESIMS, electronic circular dichroism (ECD) calculations, and single-crystal X-ray diffraction analyses. Notably, compound 1 has an undescribed tetracyclic 5/8/5/7 fused carbon skeleton, and compound 2 possesses a rare multicyclic caged ring system. The biosynthetic pathway of 1 was proposed starting from 6 via a series of oxidation and cyclization reactions. Compound 6 showed excellent antiproliferation and apoptosis induction effects against A549 cell line. Additionally, compounds 5 and 6 exhibited noticeable antimicrobial ability against Bacillus cereus, Staphylococcus aureus, and Staphylococcus epidermidis. These findings not only developed the chemical and bioactivities diversities of ophiobolin-sesterterpenoid but also provided an idea to boost the application of natural products in the control of food pathogens

    Flow cytometry analysis of bEnd.3 cells.

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    <p>Cells incubated with free FITC and QDs (1), MPLs (2), and TAT-MPLs (3) for 0.5 h, 3 h and 12 h at a NP concentration of 20 µg/mL. The NPs were labeled with FITC. The FITC (A and B) and QD fluorescence intensity (C and D) are shown.</p
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