Cramming versus threading of long amphiphilic oligomers into a polyaromatic capsule

• Published in: Nature communications 2018-10, Vol.9 (1), p.4227-10, Article 4227
• Main Authors: Yamashina, Masahiro, Kusaba, Shunsuke, Akita, Munetaka, Kikuchi, Takashi, Yoshizawa, Michito
• Format: Article
• Language: English
• Subjects: 140/131; 140/58; 639/638/541; 639/638/541/964; 639/638/541/965; Calorimetry; Crystal structure; Ethylene oxide; Humanities and Social Sciences; Hydrogen; Hydrogen bonding; Mass spectrometry; Molecular weight; multidisciplinary; NMR; Nuclear magnetic resonance; Oligomers; Science; Science (multidisciplinary); Scientific imaging; Titration; Titration calorimetry
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-018-06458-w

Oligo(ethylene oxide)s are known as widely useable yet not very interactive amphiphilic compounds. Here we report that the long amphiphilic oligomers are bound by a polyaromatic capsule in two different manners, depending on the chain length. For instance, the shorter pentamer is crammed into the isolated cavity of the capsule, whereas the longer decamer is threaded into the capsule to form a 1:1 host–guest complex in a pseudo-rotaxane fashion. These unusual bindings occur instantly, spontaneously, and quantitatively even in water at room temperature, with relatively high binding constants ( K a  > 10 6  M –1 ). Isothermal titration calorimetry (ITC) studies reveal that enthalpic stabilization is a dominant driving force for both of the complexations through multiple host–guest CH-π and hydrogen-bonding interactions. Furthermore, long oligomers with an average molecular weight of 1000 Da (e.g., 22-mer) are also threaded into the capsules to give pseudo-rotaxane-shaped 2:1 host–guest complexes in water, selectively. Molecular capsules typically bind only guests with volumes smaller than their cavities. Here, the authors find that a polyaromatic capsule accommodates linear amphiphilic oligomers in a length-dependent manner, whereas short chains are fully crammed into the cavity, long chains can be incorporated into the capsule in a threaded fashion.