Charlotte L. Stern

Although catalysis is widely exploited by nature to orchestrate noncovalent supramolecular assembly and build up complex living systems, its utilization in synthetic chemistry has conventionally been limited to accelerating covalent reactions. Consequently, the development of artificial systems for catalytic assembly remains a formidable and largely unexplored challenge. Here, we present a rationally designed strategy of electron-catalyzed supramolecular assembly, wherein the electron acts as an efficient, robust, and versatile catalyst to accelerate the formation of a donor–acceptor complex. Optimization of the elementary steps and intermediate stability yields an efficient catalytic cycle, furnishing the process with both a high turnover number and operational robustness in open air. Furthermore, the electron catalysis can be readily triggered by diverse external stimuli─including electricity, light, and mechanical force─enabling precise spatiotemporal control over the assembly process and near-quantitative synthesis of supramolecular complexes. Collectively, this work establishes a well-elucidated strategy of catalytic assembly with remarkable practicality, advancing the frontiers of noncovalent synthetic chemistry.

Mechanical bonds impart unique mechanical properties to polymers. However, forming polymers with many mechanical bonds is traditionally difficult and has limited the study of mechanically interlocked materials (MIMs) to milligram-scale amounts and/or sparse incorporation of interlocked components. We recently introduced a two-dimensional polymer architecture in which every repeat unit contains a mechanical bond through a copolymerization reaction between crystalline and diffusible monomers. Here we described a significantly accelerated variant of this polymerization that enabled scaling to >100 g batches of the polymer and the preparation of >500 g of the polymer in total using equipment found in most academic research laboratories. This polymer is produced in a two-step procedure in which a tetrafunctional phenol monomer is crystallized into a mechanically interlocked structure supported by hydrogen bonding, after which polymerization occurs by reaction with dimethyldichlorosilane in hexanes, a nonsolvent for the crystal. Improved polymerization efficiency and kinetics were realized by incorporating triethylamine, which accelerates siloxane bond formation and incorporates into the monomer crystal in a single-crystal-to-single-crystal transformation. Crystallization procedures to produce monomer crystals in 50-g batches and polymerization techniques to produce the 2D MIM in 100-g batches are reported. TPE-PhO[Si(CH₃)₂]₂ produced at these larger scales shows consistent chemical composition by X-ray photoelectron spectroscopy and NMR spectroscopy and the expected 2D morphology by scanning electron microscopy and atomic force microscopy. These findings introduce 2D MIMs as a unique yet readily accessible polymer architecture.

Precise construction of molecular heterostructures in organic donor-acceptor (D-A) cocrystals is crucial for understanding charge transfer (CT) dynamics and developing high-performance optoelectronic materials. Although cocrystals with densely packed D-A arrays have been widely investigated, discrete heterojunctions at the molecular scale have been scarcely explored. Herein, we demonstrate an approach to create what we have referred to as discrete molecular interfaces in D-A cocrystals employing a tetracationic naphthalenediimide-based macrocycle (NBox⁴⁺) and an electron-rich guest pyrene (Pyr). The large cavity of NBox⁴⁺ reduces its host-guest binding affinity with pyrene in solution but facilitates the formation of A-D-A discrete molecular interfaces in the NBox·Pyr cocrystal. The NBox·Pyr cocrystal exhibits a 20 nm red shift in UV-vis absorption and a ∼0.1 eV lower CT state energy compared to the NPy·Pyr cocrystal, formed from Pyr and the monomeric analogue (NPy²⁺) of NBox⁴⁺, which features conventional 1D alternating D-A stacks. Femtosecond transient absorption microscopy reveals a shorter CT state lifetime of 203 ps in NBox·Pyr (versus 1083 ps in NPy·Pyr), indicating faster charge recombination as a result of stronger electronic coupling at the discrete molecular interfaces in the NBox·Pyr cocrystal. This research highlights the critical role of discrete molecular interfaces in tailoring CT interactions and excited-state dynamics in the solid state, offering a powerful and versatile strategy for designing optoelectronic materials with molecular-level spatial resolution.

Hexakis(neopentyl)diruthenium(III,III) [Ru₂(CH₂CMe₃)₆ or Ru₂Np₆], first synthesized in 1984, is a d⁵-d⁵ analogue of the classic d³-d³ M₂X₆ Chisholm-type, unsupported metal-metal triply-bonded Group 6 complexes. We report an alternative synthetic route to Ru₂Np₆ and an updated low-temperature crystal structure. The Ru-Ru bond length (2.3141(3) Å) is only 0.15 Å longer than the Mo-Mo bond in Mo₂Np₆, less than might be expected upon adding four electrons. The Ru-Ru bond was originally proposed to be a triple bond, which seemed inconsistent with the usual M-M bonding model. We use DFT and TD-DFT calculations on Mo₂R₆ and Ru₂R₆ (R = Me, Np) to investigate the differences in metal-metal and metal-ligand bonding between the d³-d³ and d⁵-d⁵ systems. In the Ru₂R₆ systems, the two RuR₃ fragments adopt a pyramidalized geometry to maximize ligand-to-metal donation and to shift electron density from the strongly antibonding Ru-Ru π* orbital to the weakly bonding Ru-Ru δ orbital, thus preserving some of the Ru-Ru π bonding. In contrast, the MoR₃ fragments in Mo₂R₆ adopt a more trigonal planar geometry to preserve the Mo-Mo π bonding. The calculated and experimental UV-vis spectra are near band-for-band matches, and the energies and orbital characters of the excitations are presented.

The development of mesoporous hydrogen-bonded organic frameworks (HOFs) is critically important for various applications, yet it poses significant challenges. Herein, we present the synthesis and characterization of a robust mesoporous HOF, RP-H200, constructed through the orchestration of π-π stacking and hydrogen bonding interactions in a 2-fold interpenetrated framework. RP-H200 features a unique double-walled structure with a pore size of 3.6 nm, representing the largest pore size among reported HOFs to date. The framework exhibits a high surface area of 2313 m² g^-1, with aromatic surfaces dominating the mesoporous channels. The methane storage performance of RP-H200 reaches a high capacity of 0.31 g g^-1 at 270 K/100 bar and 0.25 g g^-1 at 296 K/100 bar. The combination of large permanent mesoporosity, excellent thermal stability, and high surface area in RP-H200 makes it a promising candidate for clean energy storage and other functions.

MNK activity is regulated by the p38 and Erk MAPK pathways. Phosphorylation of MNK leads to its activation and binding to the eIF4G/eIF4E complex. MNK then phosphorylates eIF4E at Ser209, whose activation is associated with oncogene translation, leading to tumorigenesis. Given this important role for eIF4E in tumorigenesis, MNK inhibition with novel small molecule inhibitors could be a promising strategy to combat AML, which continues to be an area of unmet medical need. Here, we report the medicinal optimization of a series of novel inhibitors and their evaluation of their effects on eIF4E and leukemia cell viability. We discovered a class of ether-containing compounds with a high MNK1/2 selectivity. These MNK inhibitors show good potency in reducing cell viability and colony formation and have desirable pharmacokinetic properties. X-ray cocrystallization was accomplished to confirm the binding mode of our inhibitors and aid in future optimization.

Helicates are a defining element of DNAs and proteins, with functions that are critical to a variety of biological processes. Cyclodextrins are promising candidates for forging multiple-stranded helicates with well-defined helicity, but a lack of available tools has precluded the construction of artificial helical nanochannels with a controllable geometry and helicity from these widely available chiral building blocks. Herein, we disclose a family of Ag₆L₂ helical nanochannels that can be readily assembled from α-cyclodextrin-derived ligands through coordination between pyridinyl groups and Ag⁺ cations. We discovered that the nanochannels exhibit either an M or a P helicity when the Ag⁺ cations adopt a tetrahedral coordination geometry while losing most of their helicity when the Ag⁺ cations are linearly coordinated. Both the geometry and helicity of the nanochannels can be precisely controlled by simply changing the number of methyl groups at the ortho positions of the pyridinyl ligands. The tetracoordinated Ag⁺ cations interconnect the helical nanochannels into an infinite two-dimensional coordinative network characterized by hexagonal tessellation. Theoretical calculations, which reveal lower energies of the helical conformations observed in crystals compared with those of their inverted counterparts, support the experimental results.

Selective crystallization of a novel thorium metal–organic framework (NU-2500) enables the efficient separation of Th( iv ) from initial mixtures with rare earth( iii ) ions.

Mechanical bonds arise between molecules that contain interlocked subunits, such as one macrocycle threaded through another. Within polymers, these linkages will confer distinctive mechanical properties and other emergent behaviors, but polymerizations that form mechanical bonds efficiently and use simple monomeric building blocks are rare. In this work, we introduce a solid-state polymerization in which one monomer infiltrates crystals of another to form a macrocycle and mechanical bond at each repeat unit of a two-dimensional (2D) polymer. This mechanically interlocked 2D polymer is formed as a layered solid that is readily exfoliated in common organic solvents, enabling spectroscopic characterization and atomic-resolution imaging using advanced electron microscopy techniques. The 2D mechanically interlocked polymer is easily prepared on multigram scales, which, along with its solution processibility, enables the facile fabrication of composite fibers with Ultem that exhibit enhanced stiffness and strength.