Encapsulation and solid state sequestration of gases by calix[6]arene-based molecular containers

Intramolecular Cation-π Interactions Organize Bowl-Shaped, Luminescent Molecular Containers

Molecules with nonplanar architectures are highly desirable due to their unique topological structures and functions. We report here the synthesis of two molecular containers (1 ⋅ 3Br- and 1 ⋅ 3Cl-), which utilize intramolecular cation-π interactions to enforce macrocylic arrangements and exhibit high binding affinity and luminescent properties. Remarkably, the geometry of the cation-π interaction can be flexibly tailored to achieve a precise ring arrangement, irrespective of the angle of the noncovalent bonds. Additionally, the C-H⋅⋅⋅Br- hydrogen bonds within the container are also conducive to stabilizing the bowl-shaped conformation. These bowl-shaped conformations were confirmed both in solution through NMR spectroscopy and in the solid state by X-ray studies. 1 ⋅ 3Br- shows high binding affinity and selectivity: F->Cl-, through C-H⋅⋅⋅X- (X=F, Cl) hydrogen bonds. Additionally, these containers exhibited blue fluorescence in solution and yellow room-temperature phosphorescence (RTP) in the solid state. Our findings illustrate the utility of cation-π interactions in designing functional molecules.

MoloVol: an easy-to-use program for analyzing cavities, volumes and surface areas of chemical structures

Cavities are a ubiquitous feature of chemical structures encountered in various fields ranging from supramolecular chemistry to molecular biology. They are involved in the encapsulation, transport and transformation of guest molecules, thus necessitating a precise and accessible tool for estimating and visualizing their size and shape. MoloVol, a free user-parametrizable open-source software, developed for calculating a range of geometric features for both unit-cell and isolated structures, is presented here. MoloVol utilizes up to two spherical probes to define cavities, surfaces and volumes. The program was optimized by combining an octree data structure with voxel-partitioned space, allowing for even high-resolution protein structure calculations on reasonable timescales. MoloVol comes with a user-friendly graphic interface along with a command-line interface for high-throughput calculations. It was written in C++ and is available on Windows, macOS and Linux distributions.

A Cavity-Tailored Metal-Organic Cage Entraps Gases Selectively in Solution and the Amorphous Solid State

Here we report the subcomponent self-assembly of a truxene-faced Zn4 L4 tetrahedron, which is capable of binding the smallest hydrocarbons in solution. By deliberately incorporating inward-facing ethyl groups on the truxene faces, the resulting partially-filled cage cavity was tailored to encapsulate methane, ethane, and ethene via van der Waals interactions at atmospheric pressure in acetonitrile, and also in the amorphous solid state. Interestingly, gas capture showed divergent selectivities in solution and the amorphous solid state. The selective binding may prove useful in designing new processes for the purification of methane and ethane as feedstocks for chemical synthesis.

Unraveling the Sorption Mechanism of CO2 in a Molecular Crystal without Intrinsic Porosity

The facile uptake of CO₂ gas in a nonporous molecular crystal constituted by long molecules with carbazole and ethynylphenyl moieties was reported in experiments recently. Herein, the mechanism of gas uptake by this crystal is elucidated using atomistic molecular simulations. The uptake of CO₂ is shown to be facilitated by (i) the capacity of the crystal to expand in volume because of weak intermolecular interactions, (ii) the parallel orientation of the long molecules in the crystal, and (iii) the ability of the molecule to marginally bend, yet not lose crystallinity because of the anchoring of the terminal carbazole groups. The retention of crystallinity upon sorption and desorption cycles is also demonstrated. At high enough pressures, near-neighbor CO₂ molecules sorbed in the crystal are found to be oriented parallel to each other.