Journal of the American Chemical Society最新文献

Dynamic covalent organic frameworks (COFs) represent an emerging class of porous materials with an inherent structural flexibility. However, due to the challenges in their synthesis and structural characterization, research on dynamic COFs remains at an early stage and requires further exploration. Herein, we report the designed synthesis of a novel COF with entangled 2D layers that exhibits interesting dynamic behavior in response to organic vapor exposure. By employing the continuous rotation electron diffraction technique, we precisely resolved the crystal structures of the COF before and after vapor adsorption. Structural analysis revealed that the vapor-induced conformational changes, such as anthracene unit rotation, triggered layer adjustments and reduced entanglement angles, leading to significant pore structure alterations. This study not only introduces a new class of dynamic COFs but also provides a foundation for the rational design of entangled frameworks with structural flexibility for diverse applications.

γ-Al₂O₃ is used as both a catalyst and a support for catalytic active phases. The properties of γ-Al₂O₃ have been ascribed to specific surface sites, with varying Al coordination number, acidity, and basicity, depending on the morphology of the material. Here, we combine surface-specific ²⁷Al{¹H} 2D high-field NMR (28.2T, 1.2 GHz for ¹H frequency) at fast MAS (50 kHz) to observe four main distinct families of surface Al-OH sites. Comparing the measured NMR signatures (²⁷Al δ_iso, C_Q, and ¹H δ_iso) to computed values from a large range of structural DFT models enables to identify specific edge and facet Al-OH surface sites in γ-Al₂O₃, including a distinct ^[4]Al-OH site with an unprecedented C_Q approaching 18 MHz. This molecular-level description of alumina surfaces opens new opportunities to understand its unique properties, such as the stabilization of small particles down to single atoms, central to catalytic processes.

Herein, we report water-intercalated and humidity-responsive lamellar materials obtained from the self-assembly of sodium acrylate (ANa)/alkyl or oleyl acrylate (RA) random copolymers. The random copolymers efficiently absorbed water into the hydrophilic ANa/main chain phase from the outer environment to form lamellar structures consisting of the water-intercalated hydrophilic segments and the hydrophobic side chains. The lamellar formation involves controlling the weight fraction of hydrophilic segments containing water to 40-70 wt % by the RA content, hydrophobic side chains, and the amount of absorbed water. The domain spacing can be controlled in the range of 2-6 nm. More interestingly, the lamellar materials reversibly afford expansion and contraction of the domain spacing in the sub-1 nm level via the absorption and release of water, in response to relative humidity. The multilayered lamellar formation process via the intercalation of water was analyzed in situ by neutron reflectometry and atomic force microscopy measurements under humid conditions. The polymer film further served as a moisture-sensitive actuator that macroscopically induces deformation responsive to humidity.

Thin-film β tungsten (β-W), a metastable phase of tungsten, holds significant potential in the fabrication of superconducting and spin-memory devices. However, due to the rapid surface passivation of tungsten in oxygen and moisture, the synthesis of nanosized metastable β-W with the intrinsic atomic surface is still difficult, and their magnetic properties remain rather unexplored. Inspired by the strong host-guest interaction-induced stabilization, we reported the synthesis of atomically thin (1.0-1.3 nm) metastable β-W nanowires within single-walled carbon nanotubes (SWCNTs) through an oxygen-assisted transformation of starting W₂C, with 85% of β-W nanowires along the anisotropic ⟨010⟩ direction. Atomically resolved electron microscopy directly unveils the dynamic evolutions of W₂C-to-β-W and further β-to-α-W within SWCNTs, depending on the H₂-annealing time. Detailed mechanistic studies by theoretical calculations and experiments reveal that oxygen diffused within the W₂C lattice governs the formation and stabilization of ultrathin β-W nanowires within the SWCNTs. Additionally, the nanoconfinement of SWCNTs, restricting the thickness of W nanowires down to 2 nm, also benefits the thermodynamically favorable nucleation of β-W than α-W. With the protection of a single graphene layer against water erosion, β-W@SWCNTs exhibit a ferromagnetic response at ∼130 K, with higher chemical stability than fully exposed thin-film β-W. This work may provide a feasible way to design the ferromagnetic nanowire metamaterials based on aligned SWCNT arrays that have the potential to fabricate microwave and spin devices.

Prussian blue analogues (PBAs) are promising cathode candidates for aqueous Na ion batteries (ANIBs) considering their low-carbon and cost-effective features. However, it is still a huge challenge to achieve desirable energy density coupled with long cycle life due to inherent Na defects in PBAs and the unstable solid-electrolyte interphase (SEI) layer. Herein, we design Na₂C₄O₄ additives as sodium supplements to compensate for Na defects in PBAs, while utilizing the CO₂ products decomposed from Na₂C₄O₄ to construct a robust SEI layer containing Na₂CO₃ species. As proof of concept, our building of full ANIBs using iron-based PBAs and NaTi₂(PO₄)₃ anode with an appropriate amount of Na₂C₄O₄ enable a reversible capacity of ∼144 mA h g^-1 at 0.2 C and an excellent cycling stability of 15,000 cycles with 85% retention at 10 C. The proposed concept is further extended to the manganese-based PBA ANIBs to deliver an energy density of 92 W h kg^-1 with improved cycling stability.

The exploration of novel and high-performance organo-electrocatalysts with well-defined active sites is vital for understanding catalytic mechanisms and replacing metal-based catalysts, but remains a formidable challenge. Here, we report metal-free trifluoroacetate as a new organo-electrocatalyst, where the strong electron-withdrawing trifluoromethyl (-CF₃) group intrinsically transforms the neighboring carboxylate anions (-COO^-) into highly efficient active sites for electrocatalytic acetylene semihydrogenation. The electrophilic acetylene molecule bonds to the negatively charged O^- sites of the carboxylate anion via the σ-configuration. Benefiting from precise molecular engineering of electron-withdrawing groups, the ethylene partial current density presents a volcano relationship with the total natural charge of the -COO^- anions. In 1 M KOH aqueous solution, trifluoroacetate delivers an ethylene partial current density of 260 mA/cm² with an ethylene Faradaic efficiency of 96.8% at -0.9 V versus the reversible hydrogen electrode (RHE) under a pure acetylene atmosphere, outperforming metal-based electrocatalysts. This work presents a new type of high-activity organo-electrocatalysts with -COO^- anions as active center and promises its application in electrocatalysis.

Vancomycin continues to be a widely used antibiotic of last resort in treating drug-resistant pathogens despite the emergence of vancomycin-resistant strains such as vancomycin-resistant Enterococci (VRE). This communication reports that conjugation of vancomycin to a second antibiotic that targets a different region of lipid II enhances and rescues its antibiotic activity. Conjugation of vancomycin to a minimal teixobactin pharmacophore in which residues 1-6 are replaced with an aromatic amide results in substantial enhancement in activity over the individual components or mixtures thereof. Three conjugates with minimum inhibitory concentrations (MICs) of 0.5 μg/mL against methicillin-resistant Staphylococcus aureus (MRSA) and 0.063-0.125 μg/mL against methicillin-susceptible Staphylococcus aureus (MSSA) were identified. Each of these conjugates is also active against VRE, even though the individual components are inactive, with the most active conjugate (Cbp-Lys₁₀-teixo_7-11-vanco) having an MIC of 2-4 μg/mL. These findings demonstrate that conjugation of vancomycin to a minimal teixobactin pharmacophore is an effective strategy for enhancing the activity of vancomycin against important Gram-positive pathogens.