Supramolecular nanoreactors featuring multiple catalytically active sites are of great importance, especially for asymmetric catalysis, and are yet challenging to construct. Here we report the design and assembly of five chiral single- and mixed-linker tetrahedral coordination cages using six dicarboxylate ligands derived-from enantiopure Mn(salen), Cr(salen) and/or Fe(salen) as linear linkers and four CpZr clusters as three-connected vertices. The formation of these cages was confirmed by a variety of techniques including single-crystal and powder X-ray diffraction, inductively coupled plasma optical emission spectrometer, quadrupole-time-of-flight mass spectrometry and energy dispersive X-ray spectrometry. The cages feature a nanoscale hydrophobic cavity decorated with the same or different catalytically active sites, and the mixed-linker cage bearing Mn(salen) and Cr(salen) species is shown to be an efficient supramolecular catalyst for sequential asymmetric alkene epoxidation/epoxide ring-opening reactions with up to 99.9% ee. The cage catalyst demonstrates improved activity and enantioselectivity over the free catalysts owing to stabilization of catalytically active metallosalen units and concentration of reactants within the cavity. Manipulation of catalytic organic linkers in cages can control the activities and selectivities, which may provide new opportunities for the design and assembly of novel functional supramolecular architectures.
We demonstrate a facile synthetic approach for preparing mixed halide perovskite (CH3NH3)Pb(Br1-xClx)3 single crystals by the solvothermal growth of stoichiometric PbBr2 and [(1 - y)CH3NH3Br + yCH3NH3Cl] DMF precursor solutions. The band gap of (CH3NH3)Pb(Br1-xClx)3 single crystals increased and the unit cell dimensions decreased with an increase in Cl content x, consistent with previous theoretical predictions. Interestingly, the Cl/Br ratio in the (CH3NH3)Pb(Br1-xClx)3 single crystals is larger than that of the precursor solution, suggesting an unusual crystal growth mechanism.
Inflammasome-dependent activation of IL-18 within the myocardium upon acute β-AR over-activation triggers cytokine cascades, macrophage infiltration and pathological cardiac remodelling. Blocking IL-18 at the early stage of β-AR insult can successfully prevent inflammatory responses and cardiac injuries.
The search for versatile heterogeneous catalysts with multiple active sites for broad asymmetric transformations has long been of great interest, but it remains a formidable synthetic challenge. Here we demonstrate that multivariate metal-organic frameworks (MTV-MOFs) can be used as an excellent platform to engineer heterogeneous catalysts featuring multiple and cooperative active sites. An isostructural series of 2-fold interpenetrated MTV-MOFs that contain up to three different chiral metallosalen catalysts was constructed and used as efficient and recyclable heterogeneous catalysts for a variety of asymmetric sequential alkene epoxidation/epoxide ring-opening reactions. Interpenetration of the frameworks brings metallosalen units adjacent to each other, allowing cooperative activation, which results in improved efficiency and enantioselectivity over the sum of the individual parts. The fact that manipulation of molecular catalysts in MTV-MOFs can control the activities and selectivities would facilitate the design of novel multifunctional materials for enantioselective processes.
Following our previous works on pure-silica-zeolite (PSZ) MFI, in this study we explore PSZ MEL as a new option for low-k dielectric films. Our motivation has been to increase the microporosity of the spin-on films by moving to structures with a framework density (FD) lower than MFI. Nanoparticle PSZ MEL suspensions were synthesized by a two-stage method that allowed the yield of nanocrystals to be significantly enhanced, while the zeolite nanocrystals remain small. For the first time zeolite nanocrystals of about 50 nm were synthesized with a yield as high as 57%. Nanoparticle suspensions with different particle sizes and crystallinities were spun on silicon wafers to prepare continuous thin films. An ultralow-k value as low as 1.5 was obtained with MEL nanoparticle suspension of high relative crystallinity. The surface roughness of the PSZ MEL film with high relative crystallinity is greatly improved (R(rms) approximately 5.6 nm) compared to MFI films with high relative crystallinity (R(rms) approximately 12 nm).
As China's first X-ray astronomical satellite, the Hard X-ray Modulation Telescope (HXMT), which was dubbed as Insight-HXMT after the launch on June 15, 2017, is a wide-band (1-250 keV) slat-collimator-based X-ray astronomy satellite with the
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