Revealing the Way of Self-Complementary Dimerization for a Shape-Persistent Macrocycle Using Density Functional Theory Calculations

A high-performance nanoporous Si/Al2O3 foam lithium-ion battery anode fabricated by selective chemical etching of the Al-Si alloy and subsequent thermal oxidation

Nanostructured micrometer-sized Al-Si particles are synthesized via a facile selective etching process of Al-Si alloy powder. Subsequent thin Al2O3 layers are introduced on the Si foam surface via a selective thermal wet oxidation process of etched Al-Si particles. The resulting Si/Al2O3 foam anodes exhibit outstanding cycling stability (a capacity retention of 78% after 300 cycles at the C/5 rate) and excellent rate capability.

Solution-phase dimerization of an oblong shape-persistent macrocycle

A new shape-persistent macrocycle comprising two 2,3-triphenylene moieties bridged by m-phenylene ethynylenes has been synthesized. UV-vis and fluorescence spectroscopies indicate limited interaction between the two triphenylene units. The compound, which has a pronounced oblong shape (the core measures approximately 2.2 × 1.0 nm), aggregates in CDCl3 and toluene-d8 to give stacked dimers, as indicated by the (1)H NMR signals corresponding to protons on or near the core, which shift upfield with increasing concentration. These changes in NMR shielding were modeled using DFT calculations on candidate dimer geometries. The best match to the experimental data was obtained for a dimer consisting of arene-arene stacking by 3.6 Å (on average) with a displacement along the molecular long axis of 3.5-4.0 Å. This displacement is larger than can be explained by the electronic effects of aromatic stacking interactions. Instead, the minimization of steric interactions between the side chains appears to control the dimer geometry, with the alkoxy groups of one molecule sliding into registry with the gaps along the periphery of the other. Such lateral displacement (as opposed to rotation) is a direct consequence of the extended oval shape of the compound.

Effects of chemical bonding on heat transport across interfaces

Interfaces often dictate heat flow in micro- and nanostructured systems. However, despite the growing importance of thermal management in micro- and nanoscale devices, a unified understanding of the atomic-scale structural features contributing to interfacial heat transport does not exist. Herein, we experimentally demonstrate a link between interfacial bonding character and thermal conductance at the atomic level. Our experimental system consists of a gold film transfer-printed to a self-assembled monolayer (SAM) with systematically varied termination chemistries. Using a combination of ultrafast pump-probe techniques (time-domain thermoreflectance, TDTR, and picosecond acoustics) and laser spallation experiments, we independently measure and correlate changes in bonding strength and heat flow at the gold-SAM interface. For example, we experimentally demonstrate that varying the density of covalent bonds within this single bonding layer modulates both interfacial stiffness and interfacial thermal conductance. We believe that this experimental system will enable future quantification of other interfacial phenomena and will be a critical tool to stimulate and validate new theories describing the mechanisms of interfacial heat transport. Ultimately, these findings will impact applications, including thermoelectric energy harvesting, microelectronics cooling, and spatial targeting for hyperthermal therapeutics.

Aromatic rings in chemical and biological recognition: energetics and structures

This review describes a multidimensional treatment of molecular recognition phenomena involving aromatic rings in chemical and biological systems. It summarizes new results reported since the appearance of an earlier review in 2003 in host-guest chemistry, biological affinity assays and biostructural analysis, data base mining in the Cambridge Structural Database (CSD) and the Protein Data Bank (PDB), and advanced computational studies. Topics addressed are arene-arene, perfluoroarene-arene, S⋅⋅⋅aromatic, cation-π, and anion-π interactions, as well as hydrogen bonding to π systems. The generated knowledge benefits, in particular, structure-based hit-to-lead development and lead optimization both in the pharmaceutical and in the crop protection industry. It equally facilitates the development of new advanced materials and supramolecular systems, and should inspire further utilization of interactions with aromatic rings to control the stereochemical outcome of synthetic transformations.