Luminescent organic porous crystals from non-cyclic molecules and their applications

Organic porous crystals from small and non-cyclic organic molecules can be constructed by various intermolecular weak interactions. Owing to their precise stacking types, intermolecular interaction and pore microstructure, the relationship...

Gas Storage in Porous Molecular Materials

Molecules with permanent porosity in the solid state have been studied for decades. Porosity in these systems is governed by intrinsic pore space, as in cages or macrocycles, and extrinsic void space, created through loose, intermolecular solid-state packing. The development of permanently porous molecular materials, especially cages with organic or metal-organic composition, has seen increased interest over the past decade, and as such, incredibly high surface areas have been reported for these solids. Despite this, examples of these materials being explored for gas storage applications are relatively limited. This minireview outlines existing molecular systems that have been investigated for gas storage and highlights strategies that have been used to understand adsorption mechanisms in porous molecular materials.

Propyne Gas Adsorption in a Cyclic Hexapeptoid: A Combined In Situ XRPD and DFTB Study*

Cyclic peptoids are macrocyclic N-substituted oligoglycines, with remarkable structural, chemical and physical properties. The gas adsorption properties of a permanently porous hexameric cyclopeptoid decorated with four propargyl and two methoxyethyl side chains were monitored by in situ X-ray powder diffraction (XRPD). High-resolution XRPD data together with Rietveld and density functional based tight binding (DFTB) method allowed us to locate propyne guest molecules inside the host channels, even though the powder sample contains more than one phase. We were able to characterize the host-guest interactions, providing useful information on the host recognition sites and discuss host adaptiveness and host-guest chemical affinity in comparison with analogous compounds.

Evolution of the Design of CH4 Adsorbents

In this review, the evolution of paradigm shifts in CH4 adsorbent design are discussed. The criteria used as characteristic of paradigms are first reports, systematic findings, and reports of record CH4 storage or deliverable capacity. Various paradigms were used such as the systematic design of micropore affinity and pore size, functionalization, structure optimization, high throughput in silico screening, advanced material property design which includes flexibility, intrinsic heat management, mesoporosity and ultraporosity, and process condition optimization. Here, the literature is reviewed to elucidate how the approach to CH4 adsorbent design has progressed and provide strategies that could be implemented in the future.

Supramolecular-Macrocycle-Based Crystalline Organic Materials

Supramolecular macrocycles are well known as guest receptors in supramolecular chemistry, especially host-guest chemistry. In addition to their wide applications in host-guest chemistry and related areas, macrocycles have also been employed to construct crystalline organic materials (COMs) owing to their particular structures that combine both rigidity and adaptivity. There are two main types of supramolecular-macrocycle-based COMs: those constructed from macrocycles themselves and those prepared from macrocycles with other organic linkers. This review summarizes recent developments in supramolecular-macrocycle-based COMs, which are categorized by various types of macrocycles, including cyclodextrins, calixarenes, resorcinarenes, pyrogalloarenes, cucurbiturils, pillararenes, and others. Effort is made to focus on the structures of supramolecular-macrocycle-based COMs and their structure-function relationships. In addition, the application of supramolecular-macrocycle-based COMs in gas storage or separation, molecular separation, solid-state electrolytes, proton conduction, iodine capture, water or environmental treatment, etc., are also presented. Finally, perspectives and future challenges in the field of supramolecular-macrocycle-based COMs are discussed.

Effect of external pressure on the release of methane through MFI zeolite nanochannels

In this work, the effects of external pressure on the release of methane through zeolite nanochannels are studied through molecular dynamics (MD) simulations. The release percentage of methane under three types of pressure loadings with various strengths and frequencies are obtained. Specifically, constant, sawtooth-shaped, and sinusoidal pressures are examined. As the pressure strength is increased, it is found that the release percentage first decreases and then increases significantly before finally approaching a constant. At sufficiently high pressures, the release percentage of methane under constant external pressure is about 65%, while it reaches over 90% for sawtooth-shaped and sinusoidal pressures. The loading frequency for periodic external pressures appears to be unimportant compared with the effect of the pressure strength. Theoretical predictions of the release percentage are made on the basis of the kinetic energy of methane molecules and the energy barrier inside the nanochannels, which are in good agreement with MD simulations.

In this work, the effects of external pressure on the release of methane through zeolite nanochannels are studied through molecular dynamics (MD) simulations.

Effects of temperature and pore structure on the release of methane in zeolite nanochannels

In this work, we investigate the effects of temperature and pore size on the release of methane in zeolite nanochannels through molecular dynamics (MD) simulations. The methane release percentage at different temperatures and for different zeolite structures is calculated. In all-silica MFI (silicalite-1) zeolite, it is found that the release percentage increases with increasing temperature roughly at a constant rate when the temperature is below 598 K. For higher temperatures, the release percentage reaches about 90% and remains almost constant. For other structures, the release percentage is greatly affected by the average pore size. The release percentage is determined by the temperature and energy barrier inside the pores. Based on the energy barriers obtained in MD simulations, theoretical predictions of the release percentage are made, which are in good agreement with numerical results.

The effects of temperature and pore size on release of methane in zeolite nanochannels is investigated by molecular dynamics simulations.

Pillar[5]arene-based supramolecular organic frameworks for highly selective CO2-capture at ambient conditions

Low-density, solid-state, porous supramolecular organic frameworks are constructed using pillarenes. The frameworks have a honeycomb-like structure, permanent porosity, high thermal stability, and selective and reversible sorption properties toward CO2. The exceptionally selective CO2-sorption properties (375/1, 339/1) of one framework over N2 and CH4 indicate potential applications in CO2-capture for post-combustion power plants and natural gas sweetening.

Supramolecular self-assemblies as functional nanomaterials

In this review, we survey the diversity of structures and functions which are encountered in advanced self-assembled nanomaterials. We highlight their flourishing implementations in three active domains of applications: biomedical sciences, information technologies, and environmental sciences. Our main objective is to provide the reader with a concise and straightforward entry to this broad field by selecting the most recent and important research articles, supported by some more comprehensive reviews to introduce each topic. Overall, this compilation illustrates how, based on the rules of supramolecular chemistry, the bottom-up approach to design functional objects at the nanoscale is currently producing highly sophisticated materials oriented towards a growing number of applications with high societal impact.

Inclusion properties of volatile organic compounds in a calixarene-based organic zeolite

The inclusion properties of a calixarene-based porous material have been studied to investigate the adsorption and the desorption of carbon tetrachloride, chloroform, and water in the zeolite-like structure. Uptake and release processes have been studied both by time-resolved powder X-ray diffraction and by thermogravimetric analysis to obtain structural and kinetic information. The selected guests are able to enter the structure with an increase in the host cell volume and with time-dependent diffusivity coefficients. Chloroform molecules act as a permanent porosity switch promoting a phase transition to non-porous triclinic form.

The CH/π hydrogen bond in chemistry. Conformation, supramolecules, optical resolution and interactions involving carbohydrates

The CH/π hydrogen bond is an attractive molecular force occurring between a soft acid and a soft base. Contribution from the dispersion energy is important in typical cases where aliphatic or aromatic CH groups are involved. Coulombic energy is of minor importance as compared to the other weak hydrogen bonds. The hydrogen bond nature of this force, however, has been confirmed by AIM analyses. The dual characteristic of the CH/π hydrogen bond is the basis for ubiquitous existence of this force in various fields of chemistry. A salient feature is that the CH/π hydrogen bond works cooperatively. Another significant point is that it works in nonpolar as well as polar, protic solvents such as water. The interaction energy depends on the nature of the molecular fragments, CH as well as π-groups: the stronger the proton donating ability of the CH group, the larger the stabilizing effect. This Perspective focuses on the consequence of this molecular force in the conformation of organic compounds and supramolecular chemistry. Implication of the CH/π hydrogen bond extends to the specificity of molecular recognition or selectivity in organic reactions, polymer science, surface phenomena and interactions involving proteins. Many problems, unsettled to date, will become clearer in the light of the CH/π paradigm.