Issue 35, 2023

Solvent-controlled formation of alkali and alkali-earth-secured cucurbituril/guest trimers

Abstract

Cucurbit[7]uril (CB[7]) encapsulates adamantyl and trimethylsilyl substituents of positively charged guests in dimethyl sulfoxide (DMSO). Unlike in water or deuterium oxide, addition of a selection of alkali and alkali-earth cations with van der Waals radii between 1.0 and 1.4 Å (Na+, K+, Ca2+, Sr2+, Ba2+ and Eu3+) to the CB[7]/guest complexes triggers their cation-mediated trimerization, a process that is very slow on the nuclear magnetic resonance (NMR) time scale. Smaller (Li+, Mg2+) or larger cations (Rb+, Cs+ or NH4+) are inert. The trimers display extensive CH–O interactions between the equatorial and pseudo-equatorial hydrogens of CB[7] and the carbonyl rim of the neighboring CB[7] unit in the trimer, and a deeply nested cation between the three interacting carbonylated CB[7] rims; a counteranion is likely perched in the shallow cavity formed by the three outer walls of CB[7] in the trimer. Remarkably, a guest must occupy the cavity of CB[7] for trimerization to take place. Using a combination of semi-empirical and density functional theory techniques in conjunction with continuum solvation models, we showed that trimerization is favored in DMSO, and not in water, because the penalty for the partial desolvation of three of the six CB[7] portals upon aggregation into a trimer is less unfavorable in DMSO compared to water.

Graphical abstract: Solvent-controlled formation of alkali and alkali-earth-secured cucurbituril/guest trimers

Supplementary files

Article information

Article type
Edge Article
Submitted
19 Apr. 2023
Accepted
08 Aug. 2023
First published
15 Aug. 2023
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2023,14, 9258-9266

Solvent-controlled formation of alkali and alkali-earth-secured cucurbituril/guest trimers

D. Lončarić, F. Movahedifar, J. R. Štoček, M. Dračínský, J. Cvačka, S. Guan, B. J. Bythell, I. Císařová, E. Masson and J. Kaleta, Chem. Sci., 2023, 14, 9258 DOI: 10.1039/D3SC02032K

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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