Acyclic Cucurbit[n]uril-Type Receptors: Optimization of Electrostatic Interactions for Dicationic Guests

Area of Science:

• Supramolecular Chemistry
• Host-Guest Chemistry
• Organic Synthesis

Background:

• Cucurbit[n]urils (CB[n]) are macrocyclic hosts with a unique structure and strong binding properties.
• Acyclic CB[n]-type hosts offer tunable structures for specific guest recognition.
• Understanding structure-affinity relationships is crucial for designing advanced host molecules.

Purpose of the Study:

• To synthesize a novel acyclic CB[n]-type host molecule.
• To investigate the effect of sulfate group placement on host-guest binding affinity.
• To characterize the synthesized host and its complexes via X-ray crystallography.

Main Methods:

• Organic synthesis of the acyclic CB[n]-type host (1).
• Optimization of sulfate group positioning on the host structure.
• Binding studies with various hydrophobic (di)ammonium guest molecules (5-23).
• X-ray crystallography of host-guest complexes (1·6a and 1·6d).

Main Results:

• Successful synthesis of the acyclic CB[n]-type host (1).
• Maximized binding affinity for hydrophobic (di)ammonium guests achieved through strategic sulfate group placement near ureidyl C═O portals.
• Detailed structural information obtained from X-ray crystal structures of complexes 1·6a and 1·6d.

Conclusions:

• The synthesized acyclic CB[n]-type host exhibits potent binding capabilities for specific guests.
• Strategic functionalization, particularly sulfate group placement, is key to enhancing host-guest interactions.
• Structural insights from crystallography validate the binding mechanism and design principles.