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Cucurbit[7]uril host-guest complexes with small polar organic guests in aqueous solution
Ian W Wyman1, Donal H Macartney
1Department of Chemistry, Queen's University, 90 Bader Lane, Kingston, ON K7L 3N6, Canada.
Organic & Biomolecular Chemistry
|May 3, 2008
Summary
Cucurbit[7]uril (CB[7]) binds small organic molecules through hydrophobic and dipole-quadrupole interactions. Cation presence, however, can reduce binding by blocking CB[7] portals.
Area of Science:
- Supramolecular Chemistry
- Host-Guest Chemistry
- Chemical Physics
Background:
- Cucurbit[n]urils (CB[n]) are macrocyclic hosts with unique cavity structures.
- Understanding host-guest interactions is crucial for molecular recognition and sensing.
- The binding mechanisms within CB[7] require detailed investigation.
Purpose of the Study:
- To determine host-guest stability constants for small neutral polar organic guests in cucurbit[7]uril (CB[7]).
- To elucidate the driving forces behind guest inclusion in CB[7].
- To investigate the influence of cations on CB[7]-guest complexation.
Main Methods:
- (1)H NMR titrations were employed to measure stability constants in aqueous solution.
- Analysis of complexation-induced chemical shift changes in guest proton resonances.
- Energy-minimization calculations to model guest orientation within the host.
Main Results:
- Stability constants depend on guest properties, indicating hydrophobic and dipole-quadrupole interactions.
- Guest dipole moments align perpendicular to the CB[7] host's quadrupole moment.
- Na(+) and K(+) cations decrease stability constants for acetone and acetophenone.
Conclusions:
- Hydrophobic and dipole-quadrupole forces govern guest binding in CB[7].
- Guest orientation within CB[7] is dictated by electrostatic and nonpolar interactions.
- Cation capping of CB[7] portals negatively impacts the stability of certain host-guest complexes.
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