Using Nuclear Magnetic Resonance Spectroscopy to Probe Hydrogels Formed by Sodium Deoxycholate

Area of Science:

• Materials Science
• Biochemistry
• Supramolecular Chemistry

Background:

• Bile acid hydrogels show potential in drug delivery and cell immobilization.
• A deeper molecular understanding is needed for rational design of improved hydrogel materials.

Purpose of the Study:

• To investigate the molecular-level structure and dynamics of bile acid hydrogels using NMR spectroscopy.
• To characterize the behavior of sodium deoxycholate (NaDC) and formic acid within the hydrogel network.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy, including spin-spin relaxation times and Saturation Transfer Difference (STD) NMR.
• Diffusion Ordered Spectroscopy (DOSY) experiments were employed to study molecular diffusion.

Main Results:

• Approximately 65% of deoxycholate molecules remain mobile within the hydrogel network under typical conditions.
• The hydrogel network comprises both acid and salt forms of deoxycholate, potentially preventing excessive precipitation.
• NMR data indicated a gel-sol transition temperature of 42 °C and revealed the dynamic, reversible association of deoxycholate molecules within the network.
• Formic acid (as formate) was found to be non-immobilized, while HDO interacts with the hydrogel network via hydrogen bonding.

Conclusions:

• The study provides molecular-level insights into the structure and dynamics of sodium deoxycholate-formic acid hydrogels.
• The dynamic nature of the deoxycholate network, with reversible association, is crucial for its stability and function.
• NMR techniques are effective tools for characterizing bile acid hydrogels and guiding the development of advanced drug delivery systems.