Amplification of Electronic Circular Dichroism—A Tool to Follow Self-Assembly of Chiral Molecular Capsules

Electronic circular dichroism (ECD) can be used to study various aspects of self-assembly (definition of stoichiometric ratios, chirality amplification during self-assembly, host-guest complexation). In this work, we show that ECD is a valuable tool for monitoring the self-assembly of chiral peptide-based capsules. By analyzing the signs, intensities, and temperature dependences of ECD bands, the effects of the non-specific processes can be separated from the restriction of intramolecular motion (RIM) caused by discrete self-assembly. Analysis of experimental and theoretical ECD spectra show that the differences between assembled and non-assembled species originate from induction of inherently chiral conformation and restriction of conformational freedom that leads to amplification of ECD signals during self-assembly of discrete species.

Resorcinarene-based Supramolecular Capsules – Supramolecular Functions and Applications

A resorcinarene is a synthetic macrocycle comprising four resorcinol molecules covalently linked by methylene bridges. The interannular bridges produce a cavitand, which possesses a bowl-shaped structure. We have developed supramolecular capsules formed through Ag(I) and Cu(I) coordination-driven self-assembly of cavitands possessing 2,2’-bipyridyl arms at the upper rim. The self-assembled capsules accommodate various molecular guests and supramolecular assemblies possessing acetoxy groups. The host-guest chemistry of the molecular capsules is applied to fabricate supramolecular polymers. This account describes the recent developments in supramolecular chemistry of resorcinarene-based coordination capsules and describes the brief history of resorcinarene-based capsules and related capsules.

Xanthene[n]arenes: Exceptionally Large, Bowl-shaped Macrocyclic Building Blocks Suitable for Self-Assembly

<div>A new class of macrocycles denoted as “xanthene[n]arenes” was synthesized. In contrast to most other macrocycles, they feature a rigid bowl-shape, required for the synthesis of cavitands and for the self-assembly to molecular capsules via non-covalent interactions. The derivatization potential of the novel macrocycles was demonstrated on the xanthene[3]arene scaffold. Beside a deep cavitand, a modified macrocycle was synthesized that self-assembles into a hydrogen-bonded tetrameric capsule. Both supramolecular systems display host-guest binding properties, demonstrating the potential of xanthene[n]arenes as a new set of macrocyclic building blocks.</div>

Xanthene[n]arenes: Exceptionally Large, Bowl-shaped Macrocyclic Building Blocks Suitable for Self-Assembly

<div>A new class of macrocycles denoted as “xanthene[n]arenes” was synthesized. In contrast to most other macrocycles, they feature a rigid bowl-shape, required for the synthesis of cavitands and for the self-assembly to molecular capsules via non-covalent interactions. The derivatization potential of the novel macrocycles was demonstrated on the xanthene[3]arene scaffold. Beside a deep cavitand, a modified macrocycle was synthesized that self-assembles into a hydrogen-bonded tetrameric capsule. Both supramolecular systems display host-guest binding properties, demonstrating the potential of xanthene[n]arenes as a new set of macrocyclic building blocks.</div>

Molecular Capsule Catalysis: Ready to Address Current Challenges in Synthetic Organic Chemistry?

Self-assembled molecular capsules, host structures that form spontaneously when their building blocks are mixed, have been known since the 1990s. They share some basic similarities with enzyme pockets, as they feature defined hydrophobic binding pockets that are able to bind molecules of appropriate size and shape. The potential to utilize such host structures for catalysis has been explored since their discovery; however, applications that solve current challenges in synthetic organic chemistry have remained limited. In this short article, we discuss the challenges associated with the use of molecular capsules as catalysts, and highlight some recent applications of supramolecular capsules to overcome challenges in synthetic organic chemistry.