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Kinetics and Mechanism of Cation‐Induced Guest Release from Cucurbit[7]uril
Author(s) -
Miskolczy Zsombor,
Megyesi Mónika,
Biczók László,
Prabodh Amrutha,
Biedermann Frank
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201905633
Subject(s) - ternary complex , chemistry , ternary operation , alkali metal , aqueous solution , dissociation (chemistry) , kinetics , kinetic energy , stereochemistry , inorganic chemistry , crystallography , computational chemistry , organic chemistry , enzyme , physics , quantum mechanics , computer science , programming language
The release of two organic guests from cucurbit[7]uril (CB7) was selectively monitored by the 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‐dimethyldiazapyrenium shows a cation‐independent complex dissociation mechanism coupled to deceleration of the ingression in the presence of alkali and alkaline earth cations (M n + ) due to competitive formation of CB7–M n + 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 complex B + –CB7–M n + was unambiguously revealed. A difference of more than two orders of magnitude was found in the equilibrium constants of M n + binding to B + –CB7 inclusion complex. Large cations, such as K + and Ba 2+ , also promoted B + expulsion from the ternary complex in a bimolecular process. This study reveals a previously hidden mechanistic picture and motivates systematic kinetic investigations of other host–guest systems.