Binding Between Cyclohexanohemicucurbit[n]urils and Polar Organic Guests

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Host-Guest Chemistry

Background:

• Cyclohexanohemicucurbit[n]urils (cycHC[n]) are chiral, barrel-shaped macrocyclic hosts.
• Previous studies showed cycHC[n] bind zinc porphyrins and trifluoroacetic acid externally in halogenated solvents.

Purpose of the Study:

• To investigate the binding preferences of homologous cycHC[6] and cycHC[8] for various organic guests.
• To determine the factors influencing the binding strength and stoichiometry of host-guest complexes.
• To explore the potential of cycHC[n] as hydrogen-bonded complex acceptors.

Main Methods:

• Testing eighteen organic guests including thiophenols, phenols, carboxylic acids, and sulfonic acids.
• Characterizing guests by Hirshfeld partial charges on acidic hydrogens.
• Analyzing binding interactions using 1H and 19F NMR titrations.
• Studying complex formation with halogen anions (Cl-, Br-) in methanol and chloroform via 1H NMR.

Main Results:

• Binding strength is influenced by complex stoichiometry, partial atomic charge on the hydrogen bond donor, and guest bulkiness.
• Evidence suggests external binding with stoichiometry exceeding 2:1 for both cycHC[6] and cycHC[8].
• Complexation with halogen anions (Cl-, Br-) was not confirmed.

Conclusions:

• Cyclohexanohemicucurbit[n]urils demonstrate a preference for hydrogen bond-donating molecules.
• The study expands the application scope of cycHC[n] as multisite hydrogen bond acceptors.
• Binding is complex, influenced by multiple guest and host factors.