62 research outputs found

    Influence of C–H···O Hydrogen Bonds on Macroscopic Properties of Supramolecular Assembly

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    For CH···O hydrogen bonds in assembled structures and the applications, one of the critical issues is how molecular spatial structures affect their interaction modes as well as how to translate the different modes into the macroscopic properties of materials. Herein, coumarin-derived isomeric hydrogelators with different spatial structures are synthesized, where only nitrogen atoms locate at the <i>ortho</i>, <i>meso</i>, or <i>para</i> position in the pyridine ring. The gelators can self-assemble into single crystals and nanofibrous networks through CH···O interactions, which are greatly influenced by nitrogen spatial positions in the pyridine ring, leading to the different self-assembly mechanisms, packing modes, and properties of the nanofibrous networks. Typically, different cell proliferation rates are obtained on the different CH···O bonds driving nanofibrous structures, implying that tiny variation of the stereo-position of nitrogen atoms can be sensitively detected by cells. The study paves a novel way to investigate the influence of isomeric molecular assembly on macroscopic properties and functions of materials

    Chiral Metal–Organic Framework Decorated with TEMPO Radicals for Sequential Oxidation/Asymmetric Cyanation Catalysis

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    A chiral porous metal–organic framework (MOF) decorated with radicals has been successfully constructed by cocrystallizing achiral (2,2,6,6-tetramethylpiperidin-1-yl)­oxyl (TEMPO)-substituted tricarboxylate and enantiopure VO­(salen)-derived dipyridine ligands. The chiral MOF can function as an efficient heterogeneous catalyst for the sequential alcohol oxidation/asymmetric cyanation of aldehyde reactions with enhanced activity and enantioselectivity compared to the homogeneous counterpart

    Supramolecular Engineering of Discrete Pt(II)···Pt(II) Interactions for Visible-Light Photocatalysis

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    Visible-light photosensitizers have emerged as a sustainable and environmentally friendly medium for organic transformation. Herein, we have developed a supramolecular strategy for manipulating visible-light photosensitization and photocatalytic efficiencies. With the elaborate manipulation of aggregated Pt­(II)···Pt­(II) interactions, the discrete tetranuclear Pt complexes not only show high binding affinity (<i>K</i><sub>a</sub> ∼ 10<sup>6</sup> M<sup>–1</sup>) but also feature bathochromic-shifted metal–metal-to-ligand charge transfer transitions. Both factors are crucial for their <sup>1</sup>O<sub>2</sub> generation capability upon low-energy visible-light irradiation (λ ≥ 590 nm). More interestingly, when a terpyridine moiety is embedded in the structure of a supramolecular photosensitizer, breakup of tetranuclear Pt­(II)···Pt­(II) complexation can be realized upon addition of Zn­(OTf)<sub>2</sub>. As a consequence, photo-oxidation of a secondary amine to the corresponding imine can be deactivated and reactivated, via the sequential addition of Zn­(OTf)<sub>2</sub> and unsubstituted terpyridine as the competitive ligand. Hence, the current study proves that intelligent visible-light photocatalysts can be achieved via rational supramolecular design

    Supramolecular Cross-Linking and Gelation of Conjugated Polycarbazoles via Hydrogen Bond Assisted Molecular Tweezer/Guest Complexation

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    Supramolecular cross-linking and gelation represent a fascinating approach to improve the performance of π-conjugated polymers. Up to now, supramolecular π-conjugated polymer networks have been mainly developed by grafting noncovalent recognition motifs onto the side-chain of π-conjugated polymers. In comparison, much less attention has been paid to the construction of main-chain-type supramolecular polymer networks, in which π-conjugated polymers themselves serve as the noncovalent linkages. Herein we have developed a novel and efficient strategy to attain this objective. The design principle is primarily on the basis of noncovalent molecular recognition between bis­[alkynyl­platinum­(II)]­terpyridine molecular tweezer receptor and <i>NH</i>-type carbazole guest, which shows enhanced binding affinity due to the cooperative participation of donor–acceptor and intermolecular N–H---N hydrogen-bonding interactions. The “hydrogen-bond enhanced molecular tweezer/guest recognition” strategy can be further applied for multivalent complexation between π-conjugated polycarbazoles and homoditopic molecular tweezer cross-linker, leading to the formation of main-chain-type supramolecular polymer networks and gels with thermal and solvent responsiveness. Hence, π-conjugated polymers can be endowed with excellent processability via the supramolecular engineering approach, which provides a new avenue toward flexible optoelectronic applications

    Design and Assembly of Chiral Coordination Cages for Asymmetric Sequential Reactions

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    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 Cp<sub>3</sub>Zr<sub>3</sub> 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

    Receiver-operating characteristic curves to predict heart failure patients.

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    <p>(A), ROC curves of HSP70 for diagnosing stage B HF. (B), ROC curves of NT-proBNP for diagnosing stage B HF. HSP70 has a high sensitive cut-off value (2.72 ng/mL) in predicting stage B HF, while NT-proBNP hasn’t. (C), ROC curves of HSP70 for diagnosing stage C HF. (D), ROC curves of NT-proBNP for diagnosing stage C HF. NT-proBNP has a more sensitive cut-off value in diagnosing stage C HF (92.9%) while HSP70 has a more specific one (84.6%).</p

    Mechanically Linked Poly[2]rotaxanes Constructed via the Hierarchical Self-Assembly Strategy

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    Mechanically linked poly[2]­rotaxanes have been successfully constructed via the hierarchical self-assembly strategy. The integration of two noninterfering noncovalent recognition motifs facilitates chain extension of the B21C7-based [2]­rotaxane monomer, demonstrating the capabilities to form self-standing films with preferable transparency and softness

    The expressions of HSP 70, HSP 90 and HSP 27 in the hearts from mice subjected to ISO or vehicle at 3days,7 days, 14days and 84 days.

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    <p>The levels of Hsp 70, Hsp 90 and Hsp 27 in hearts protein extracts were examined by Western blotting. A representative Western blot from three independent experiments is shown. EIF-5 was used as an internal control.</p

    Chiral DHIP-Based Metal–Organic Frameworks for Enantioselective Recognition and Separation

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    Two chiral porous 2,3-dihydroimidazo­[1,2-<i>a</i>]­pyridine (DHIP)-based metal–organic frameworks (MOFs) are assembled from an enantiopure dipyridyl-functionalized DHIP bridging ligand. The Zn-DHIP MOF shows a good enantioseparation performance toward aromatic sulfoxides, and the heterogeneous adsorbent can be readily recovered and reused without significant degradation of the separation performance

    Multivariate Metal–Organic Frameworks as Multifunctional Heterogeneous Asymmetric Catalysts for Sequential Reactions

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    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
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