Beta-cyclodextrin host-guest complexes probed under thermodynamic equilibrium: thermodynamics and AFM force...

Area of Science:

• Supramolecular chemistry
• Surface science
• Biophysics

Background:

• Host-guest complexation is fundamental in molecular recognition.
• Beta-cyclodextrin (beta-CD) is a key host molecule with diverse applications.
• Understanding binding forces at the single-molecule level is crucial for designing molecular systems.

Purpose of the Study:

• To measure the rupture forces of individual host-guest complexes.
• To investigate the relationship between force, binding energy, and molecular structure.
• To develop a model correlating pull-off forces with thermodynamic binding parameters.

Main Methods:

• Single molecule force spectroscopy (SMFS) using atomic force microscopy (AFM).
• Functionalization of AFM tips with beta-cyclodextrin heptathioether monolayers.
• Immobilization of various guest molecules (anilyl, toluidyl, tert-butylphenyl, adamantylthiols) on surfaces.
• Analysis of force-displacement curves and pull-off force histograms.

Main Results:

• Distinct force quanta were observed for different guests, characteristic of their interaction with beta-CD.
• Pull-off forces were independent of loading rate, suggesting thermodynamic control.
• Measured rupture forces correlated with free binding energies (ΔG°) obtained from microcalorimetry and SPR.
• A quantitative model was developed linking pull-off force to binding energy.

Conclusions:

• SMFS provides quantitative insights into host-guest complex rupture forces.
• The study establishes a link between single-molecule mechanics and thermodynamics.
• The developed model aids in predicting and understanding molecular interactions at interfaces.