Covalent organic frameworks (COFs) have emerged as a novel platform for material design and functional explorations, but it remains a challenge to synthetically functionalize targeted structures for task-specific applications. Optically pure 1,1′-bi-2-naphthol (BINOL) is one of the most important sources of chirality for organic synthesis and materials science, but it has not yet been used in construction of COFs for enantioselective processes. Here, by elaborately designing and choosing an enantiopure BINOL-based linear dialdehyde and a tris(4-aminophenyl)benzene derivative or tetrakis(4-aminophenyl)ethene as building blocks, two imine-linked chiral fluorescent COFs with a 2D layered hexagonal or tetragonal structure are prepared. The COF containing flexible tetraphenylethylene units can be readily exfoliated into ultrathin 2D nanosheets and electrospun to make free-standing nanofiber membrane. In both the solution and membrane systems, the fluorescence of COF nanosheets can be effectively quenched by chiral odor vapors via supramolecular interactions with the immobilized BINOL moieties, leading to remarkable chiral vapor sensors. Compared to the BINOL-based homogeneous and membrane systems, the COF nanosheets exhibited greatly enhanced sensitivity and enantioselectivity owing to the confinement effect and the conformational rigidity of the sensing BINOL groups in the framework. The ability to place such a useful BINOL chiral auxiliary inside open channels of COFs capable of amplifying chiral discrimination of the analytes represents a major step toward the rational synthesis of porous molecular materials for more chirality applications.
Nuclear delivery and accumulation are very important for many anticancer drugs that interact with DNA or its associated enzymes in the nucleus. However, it is very difficult for neutrally and negatively charged anticancer drugs such as 10-hydroxycamptothecine (HCPT). Here we report a simple strategy to construct supramolecular nanomedicines for nuclear delivery of dual synergistic anticancer drugs. Our strategy utilizes the coassembly of a negatively charged HCPT-peptide amphiphile and the positively charged cisplatin. The resulting nanomaterials behave as the "Trojan Horse" that transported soldiers (anticancer drugs) across the walls of the castle (cell and nucleus membranes). Therefore, they show improved inhibition capacity to cancer cells including the drug resistant cancer cell and promote the synergistic tumor suppression property in vivo. We envision that our strategy of constructing nanomaterials by metal chelation would offer new opportunities to develop nanomedicines for combination chemotherapy.
Microporous covalent organic frameworks (COFs) hold great potential for small molecule separation but are yet challenging to design and synthesize. Here we report a framework interpenetration strategy to make microporous COFs for efficient separations of C8 alkyl-aromatic isomers. Two pairs of microporous three-dimensional (3D) salen- and Zn(salen)-based COFs are prepared by Schiff-base condensation of ethanediamine with tetrahedral tetra(salicylaldehyde)-silane or -methane derivatives in the presence or absence of metal ions. The four 3D COFs are isostructural and have a 7-fold interpenetrated diamondoid open framework with less than 8.0 Å wide tubular channels. They exhibit permanent porosity, high thermal stability, and good chemical resistance. The two COFs functionalized with uncoordinated salen groups can serve as stationary phases for high-performance liquid chromatography to provide baseline separation of xylene isomers and ethylbenzene with excellent column efficiency and precision, whereas the COFs with Zn(salen) motifs cannot achieve high-resolution separation. The salen-COFs showed high affinity to the o-xylene, allowing fast and selective separation of the o-isomer from the other isomers within 7 min. This is the first report utilizing COFs to separate the practically important aromatic isomers. This work highlights new opportunities in designing microporous COFs and paves the way to expand the potential applications of COF materials.
We demonstrate that the incorporation of one or two amino acids of phenylalanine (F) or 4-fluoro phenylalanine ((f)F) will greatly lower the background fluorescence intensities of conventional quenched probes with quenchers. This enhanced quenching effect was due to the synergetic effect of the aggregation caused quenching and the presence of a quencher. Such strategy will not greatly affect the enzyme recognition properties to the probes. We also demonstrated that our self-assembled nanoprobe with the enhanced quenching effect showed a better performance in cells for the detection of cell apoptosis than the unassembled probes. Our study demonstrates that using molecular self-assembly can optimize and improve the performance of molecular probes and it provides a simple but very useful strategy to boost the signal-to-noise ratios of fluorescence probes.
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