L. Biczók, Z. Miskolczy, M. Megyesi, A. Prabodh, F. Biedermann, Chem. Eur. J. 2020, Acccepted Manuscript.
This publication has been highlighted in the article "Salt-Induced Release from Macrocycles" on chemistryview.org!
The exit of two organic guests from cucurbituril (CB7) was selectively monitored by stopped?flow method in aqueous solutions of inorganic salts to reveal the mechanistic picture in detail. Two contrasting mechanisms were identified: The symmetric dicationic 2,7?dimethyl?diazapyrenium shows a cation?independent complex dissociation mechanism coupled to a deceleration of the ingression in the presence of alkali and alkaline earth cations (Mn+) due to competitive formation of CB7?Mn+ complexes. A much richer, unprecedented kinetic behaviour was observed for the ingression and egression of the monocationic and non?symmetric berberine (B+). The formation of ternary B+?CB7?Mn+ complex was undoubtedly revealed. More than two orders of magnitude difference were found in the equilibrium constants of Mn+ binding to B+?CB7 inclusion complex. Large cations, such as K+ and Ba2+, promoted B+ expulsion also in a bimolecular process from the ternary complex. This study reveals a priorly hidden mechanistic picture and motivates systematic kinetic investigations of other host?guest systems.