Microcalorimetry of chiral surfactant-cyclodextrin interactions

Area of Science:

• Supramolecular Chemistry
• Physical Chemistry
• Analytical Chemistry

Background:

• Chiral surfactants and cyclodextrins are crucial in separation science and drug delivery.
• Understanding their interactions is key to optimizing their applications.

Purpose of the Study:

• To investigate the binding interactions between chiral surfactants taurodeoxycholate (TDOCA) and deoxycholate (DOCA) with various cyclodextrins (CDs).
• To elucidate the impact of these interactions on surfactant aggregation behavior.

Main Methods:

• Isothermal titration microcalorimetry (ITMC) was employed to study the thermodynamics of complexation.
• Direct binding titrations were performed to confirm interactions.
• The study focused on TDOCA and DOCA with α-, β-, methyl-β-, hydroxypropyl-β-, and γ-cyclodextrins in aqueous solutions.

Main Results:

• TDOCA forms 1:1 host-guest complexes with β-cyclodextrin, methyl-β-cyclodextrin, hydroxypropyl-β-cyclodextrin, and γ-cyclodextrin, but not α-cyclodextrin.
• Complexation influences the apparent critical micelle concentration (cmc) and enthalpy of demicellization of TDOCA.
• Higher cyclodextrin concentrations suggest potential 2:1 cyclodextrin/TDOCA complexation.
• Similar interactions were observed for DOCA, though complicated by gel formation.

Conclusions:

• The study confirms specific host-guest complexation between chiral surfactants and cyclodextrins.
• These interactions can modulate surfactant self-assembly, impacting solubility and micelle formation.
• The findings provide insights into the mechanisms behind enhanced chiral resolution in mixed surfactant-cyclodextrin systems.