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Cucurbit[7]uril: surfactant host-guest complexes in equilibrium with micellar aggregates
Marcia Pessêgo1, Nuno Basilio, Jose A Moreira
1Departamento de Química Física y Centro Singular de Investigación en Química Biológica y Materiales Moleculares, Universidad de Santiago, 15782 Santiago, Spain.
Summary
Cucurbit[7]uril (CB7) forms stronger host-guest complexes with cationic surfactants than beta-cyclodextrin (β-CD), with CB7 binding constants independent of surfactant chain length, unlike β-CD.
Area of Science:
- Supramolecular Chemistry
- Physical Organic Chemistry
- Host-Guest Chemistry
Background:
- Host-guest complexation plays a crucial role in various chemical and biological processes.
- Beta-cyclodextrin (β-CD) and cucurbit[7]uril (CB7) are well-known macrocyclic hosts with distinct cavity properties.
- Cationic surfactants are widely used in formulations and their interactions with hosts are of significant interest.
Purpose of the Study:
- To compare the host-guest complex formation between β-CD and CB7 with a series of cationic surfactants.
- To investigate the influence of surfactant hydrophobic chain length on binding constants.
- To elucidate the driving forces behind the observed complexation behaviors.
Main Methods:
- Studied the hydrolysis of 4-methoxybenzenesulfonyl chloride (MBSC) as a model reaction.
- Employed a series of cationic surfactants with varying hydrocarbon chain lengths (C6-C18).
- Determined binding constants for β-CD and CB7 complexes with the surfactants.
Main Results:
- CB7 binding constants were independent of the surfactant's alkyl chain length.
- β-CD binding constants showed a clear dependence on the surfactant's hydrophobic character.
- CB7 exhibited significantly higher binding constants than β-CD, attributed to electrostatic interactions.
Conclusions:
- CB7 demonstrates strong, chain-length-independent binding with cationic surfactants, driven by electrostatic interactions.
- The hydrophobic effect is a dominant factor in β-CD complexation with these surfactants.
- A dynamic equilibrium exists between uncomplexed CB7 and cationic micelles, influenced by surfactant hydrophobicity.
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