Semiconductor quantum-well structures and superlattices are key building blocks in modern optoelectronics, but it is difficult to simultaneously realize defect-free epitaxial growth while fine tuning ...the chemical composition, layer thickness and band structure of each layer to achieve the desired performance. Here we demonstrate the modulation of the electronic structure-and consequently the optical properties-of organic semiconducting building blocks that are incorporated between the layers of perovskites through a facile solution processing step. Self-aggregation of the conjugated organic molecules is suppressed by functionalization with sterically demanding groups and single crystalline organic-perovskite hybrid quantum wells (down to one-unit-cell thick) are obtained. The energy and charge transfers between adjacent organic and inorganic layers are shown to be fast and efficient, owing to the atomically flat interface and ultrasmall interlayer distance of the perovskite materials. The resulting two-dimensional hybrid perovskites are very stable due to protection given by the bulky hydrophobic organic groups.
Bacterial infection, tissue hypoxia and inflammatory response can hinder the infected wound repair process. To mitigate the above issues, tannic acid-chelated Fe-decorated molybdenum disulfide ...nanosheets (MoS2@TA/Fe NSs) with dual enzyme activities were developed and anchored to a multifunctional hydrogel. The hydrogel exhibited excellent antibacterial ability owing to the combined effects of photothermal therapy (PTT), glutathione (GSH) loss, and the peroxidase (POD)-like activity (catalyse H2O2 into ·OH under acid condition) of MoS2@TA/Fe NSs. Benefitting from the catalase (CAT)-like activity, the hydrogel could decompose H2O2 into O2 at neutral pH to relieve hypoxia and supply adequate O2. POD-like activity was mainly attributed to MoS2 NSs, while CAT-like activity was primarily due to TA/Fe complex. Moreover, MoS2@TA/Fe NSs endowed the hydrogel with outstanding anti-oxidant ability to scavenge redundant reactive oxygen species (ROS) and reactive nitrogen species (RNS) under neutral environment to maintain the balance of antioxidant systems and prevent inflammation. In addition, the hydrogel could inhibit the release of inflammatory factors for the anti-inflammatory property of TA. TA retained partial phenolic hydroxyl groups, which cross-linked the nanosheets to the network structure of the hydrogel and promoted the adhesion of hydrogels. Due to the dynamic boron ester bonds between polyvinyl alcohol (PVA), dextran (Dex), MoS2@TA/Fe, and borax, the hydrogel demonstrated fast self-healing and rapid shape adaptability. This shape-adaptable adhesive hydrogel could fill the whole wound and closely contact the wound, ensuring that it achieved its functions with maximum efficiency. The MoS2@TA/Fe nanozyme-anchored multifunctional hydrogel showed high potential for bacteria-infected wound healing.
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•MoS2@TA/Fe NSs presents POD- and CAT-like activities.•MoS2@TA/Fe NSs shows anti-oxidant and anti-inflammation abilities.•The hydrogel shows fast self-healing, adhesiveness, and rapid shape-adaptivity.•MoS2@TA/Fe NSs-based hydrogel exhibits large potential in infected wound healing.
Complex materials often exhibit a hierarchical structure with an intriguing mechanism responsible for the 'propagation' of order from the molecular to the nano- or micro-scale level. In particular, ...the chirality of biological molecules such as nucleic acids and amino acids is responsible for the helical structure of DNA and proteins, which in turn leads to the lack of mirror symmetry of macro-bio-objects. To fully understand mechanisms of cross-level order transfer there is an intensive search for simpler artificial structures exhibiting hierarchical arrangement. Here we present complex systems built of achiral molecules that show four levels of structural chirality: layer chirality, helicity of a basic repeating unit, mesoscopic helix and helical filaments. The structures are identified by a combination of hard and soft x-ray diffraction measurements, optical studies and theoretical modelling. Similarly to many biological systems, the studied materials exhibit a coupling between chirality at different levels.
Two-dimensional (2D) nanomaterials have received increasing interest for many applications such as biomedicine and nanotechnology. Here, we report a facile strategy to prepare highly flexible 2D ...crystalline nanosheets with only ∼6 nm thickness from poly(ethylene glycol)-block-poly(N-octylglycine) (PEG-b-PNOG) diblock copolymer in high yield. To our best knowledge, this is the first report of free-floating, 2D extended nanosheets from polypeptoid-based block copolymers. The faceted nanostructures are achieved from hierarchical self-assembly through a sphere-to-cylinder-to-nanosheet transition pathway. The preliminary assembled spheres can behave like a fundamental packing motif to spontaneously stack into a 2D lattice via an intermediate cylinder structure, driven by crystallization of PNOG domains. The nanosheet formation process follows theoretical model for morphology development of crystalline block copolymers in selective solvents. Particularly remarkable is that we obtained the hierarchical nanostructure from synthetic block copolymers through a multiple-step strategy mimetic to protein crystallization. This is fairly distinct from the previously reported crystalline nanosheets. The ability to efficiently create 2D crystals from synthetic polymers by spontaneous assembly will enable new generations of bioinspired nanomaterials for a variety of potential applications in biomedicine and nanotechnology.
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The use of ginsenosides in cancer therapy has been intensively investigated. The ginsenoside Rh4 (Rh4), a rare saponin obtained from Panax notoginseng, dissolves in water more readily ...than total saponins, making this compound easier to use in anti-cancer pharmaceutics. Here, we investigated the antiproliferative activity and mechanisms of Rh4 in colorectal cancer, both in vivo and in vitro. A colorectal cancer xenograft model showed that Rh4 significantly inhibited tumor growth with few side effects. CCK-8 assays, flow cytometric analysis, Western blotting and immunohistochemistry revealed that Rh4 effectively suppressed colorectal cancer cell proliferation via inducing G0/G1 phase arrest, caspase-dependent apoptosis and autophagic cell death but was not significantly cytotoxic to normal colon epithelial cells. Furthermore, apoptosis played a dominant role in Rh4-induced cell death, as the pan-caspase inhibitor Z-VAD-FMK blocked cell death to a greater extent than the autophagy inhibitor 3-methyladenine. Moreover, Rh4 increased reactive oxygen species (ROS) accumulation and subsequently activated the JNK-p53 pathway. An ROS scavenger and JNK and p53 inhibitors significantly attenuated Rh4-induced apoptosis and autophagy. Thus, the present study is the first to illustrate that Rh4 triggers apoptosis and autophagy via activating the ROS/JNK/p53 pathway in colorectal cancer cells, providing basic scientific evidence that Rh4 shows great potential as an anti-cancer agent.
The electronic character of porphyrin active sites for electrocatalytic reduction of CO2 to CO in a two-dimensional covalent organic framework (COF) was tuned by modification of the reticular ...structure. Efficient charge transport along the COF backbone promotes electronic connectivity between remote functional groups and the active sites and enables the modulation of the catalytic properties of the system. A series of oriented thin films of these COFs was found to reduce CO2 to CO at low overpotential (550 mV) with high selectivity (faradaic efficiency of 87%) and at high current densities (65 mA/mg), a performance well beyond related molecular catalysts in regard to selectivity and efficiency. The catalysts are stable for more than 12 h without any loss in reactivity. X-ray absorption measurements on the cobalt L-edge for the modified COFs enable correlations between the inductive effects of the appended functionality and the electronic character of the reticulated molecular active sites.
Conventional epitaxy of semiconductor films requires a compatible single crystalline substrate and precisely controlled growth conditions, which limit the price competitiveness and versatility of the ...process. We demonstrate substrate-tolerant nano-heteroepitaxy (NHE) of high-quality formamidinium-lead-tri-iodide (FAPbI
) perovskite films. The layered perovskite templates the solid-state phase conversion of FAPbI
from its hexagonal non-perovskite phase to the cubic perovskite polymorph, where the growth kinetics are controlled by a synergistic effect between strain and entropy. The slow heteroepitaxial crystal growth enlarged the perovskite crystals by 10-fold with a reduced defect density and strong preferred orientation. This NHE is readily applicable to various substrates used for devices. The proof-of-concept solar cell and light-emitting diode devices based on the NHE-FAPbI
showed efficiencies and stabilities superior to those of devices fabricated without NHE.
A key challenge in the field of electrochemical carbon dioxide reduction is the design of catalytic materials featuring high product selectivity, stability, and a composition of earth-abundant ...elements. In this work, we introduce thin films of nanosized metal–organic frameworks (MOFs) as atomically defined and nanoscopic materials that function as catalysts for the efficient and selective reduction of carbon dioxide to carbon monoxide in aqueous electrolytes. Detailed examination of a cobalt–porphyrin MOF, Al2(OH)2TCPP-Co (TCPP-H2 = 4,4′,4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrabenzoate) revealed a selectivity for CO production in excess of 76% and stability over 7 h with a per-site turnover number (TON) of 1400. In situ spectroelectrochemical measurements provided insights into the cobalt oxidation state during the course of reaction and showed that the majority of catalytic centers in this MOF are redox-accessible where Co(II) is reduced to Co(I) during catalysis.
We present a strategy whereby selective formation of imine covalent organic frameworks (COFs) based on linking of triangles and squares into the fjh topology was achieved by the conformational design ...of the building units. 1,3,5-Trimethyl-2,4,6-tris(4-formylphenyl)benzene (TTFB, triangle) and 1,1,2,2-tetrakis(4-aminophenyl)ethene (ETTA, square) were reticulated into (TTFB)4(ETTA)3 imine , termed COF-790, which was fully characterized by spectroscopic, microscopic, and X-ray diffraction techniques. COF-790 exhibits permanent porosity and a Brunauer–Emmett–Teller (BET) surface area of 2650 m2 g–1. Key to the formation of this COF in crystalline form is the pre-designed conformation of the triangle and the square units to give dihedral angles in the range of 75–90°, without which the reaction results in the formation of amorphous product. We demonstrate the versatility of our strategy by also reporting the synthesis and characterization of two isoreticular forms of COF-790, COF-791 and COF-792, based on other square building units.
The band edges of metal-halide perovskites with a general chemical structure of ABX
(A, usually a monovalent organic cation; B, a divalent cation; and X, a halide anion) are constructed mainly of the ...orbitals from B and X sites. Hence, the structural and compositional varieties of the inorganic B-X framework are primarily responsible for regulating their electronic properties, whereas A-site cations are thought to only help stabilize the lattice and not to directly contribute to near-edge states. We report a π-conjugation-induced extension of electronic states of A-site cations that affects perovskite frontier orbitals. The π-conjugated pyrene-containing A-site cations electronically contribute to the surface band edges and influence the carrier dynamics, with a properly tailored intercalation distance between layers of the inorganic framework. The ethylammonium pyrene increased hole mobilities, improved power conversion efficiencies relative to that of a reference perovskite, and enhanced device stability.
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