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Different and Often Opposing Forces Drive the Encapsulation and Multiple Exterior Binding of Charged Guests to a M 4 L 6 Supramolecular Vessel in Water
Author(s) -
Sgarlata Carmelo,
Mugridge Jeffrey S.,
Pluth Michael D.,
Zito Valeria,
Arena Giuseppe,
Raymond Kenneth N.
Publication year - 2017
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.201703202
Subject(s) - supramolecular chemistry , chemistry , entropy (arrow of time) , isothermal titration calorimetry , catalysis , calorimetry , ammonium , ion , chemical physics , nanotechnology , combinatorial chemistry , thermodynamics , molecule , materials science , organic chemistry , physics
The supramolecular assembly [Ga 4 L 6 ] 12− acts as a nanoscale flask to mediate the reactivity of encapsulated reactive guests and also functions as a catalyst to carry out enzyme‐like chemical transformations. The guest binding to the interior cavity and exterior of this host is difficult to untangle because multiple equilibria occur in solution, and only when refining simultaneously data obtained from different techniques, such as NMR, UV/Vis, and calorimetry, can the accurate solution thermodynamics of these host–guest systems be determined. This study reports the driving forces for the inclusion and stepwise exterior guest binding of different aliphatic quaternary ammonium guests to the [Ga 4 L 6 ] 12− assembly. Encapsulation into the host cavity was found to be an entropy‐driven process, whereas exterior ion association is driven either by enthalpically favorable attractive forces or by the entropy gain due to desolvation, depending on guest size and character. The analysis of the energetics of reaction may help predicting and understanding the intimate role and contribution of the transition state in those rate‐accelerated reactions involving this supramolecular assembly as an enzyme‐like molecular flask.