Binding Studies of Cucurbit[7]uril with Gold Nanoparticles Bearing Different Surface Functionalities

Area of Science:

• Supramolecular chemistry
• Nanoparticle functionalization
• Host-guest chemistry

Background:

• Cucurbiturils (CBs) are macrocyclic hosts with unique binding properties.
• Gold nanoparticles (AuNPs) are widely used in various applications due to their tunable properties.
• Understanding host-guest interactions at the nanoscale is crucial for designing advanced materials.

Purpose of the Study:

• To quantify the host-guest interactions between cucurbit[7]uril (CB[7]) and functionalized gold nanoparticles (AuNPs).
• To investigate the influence of ligand functional groups on the binding affinity between CB[7] and AuNPs.

Main Methods:

• Isothermal titration calorimetry (ITC) was employed to measure binding thermodynamics.
• Gold nanoparticles were synthesized and functionalized with benzylamine derivatives.
• Ligands varied in the nature of the headgroup (tertiary vs. quaternary amine) and substituents on the benzene ring.

Main Results:

• The binding affinity of AuNPs to CB[7] was found to be independent of electron-donating or withdrawing groups at the para position of the benzene ring.
• Headgroups with a permanent positive charge exhibited a ten-fold increase in binding affinity compared to monomethyl counterparts.
• This highlights the critical role of electrostatic interactions in the CB[7]-AuNP system.

Conclusions:

• Permanent positive charges on AuNP ligands significantly enhance binding to cucurbituril receptors.
• The nature of the headgroup charge is a dominant factor in CB[7]-AuNP interactions, outweighing electronic effects of aromatic substituents.
• These findings provide valuable insights for designing targeted drug delivery systems and sensors utilizing supramolecular recognition.