Temperature effect on formation of sodium cholate micelles

Area of Science:

• Physical Chemistry
• Colloid and Surface Science
• Biophysical Chemistry

Background:

• Sodium cholate (NaC) is a bile salt with amphipathic properties.
• Understanding micellization is crucial for drug delivery and biological systems.
• The behavior of NaC micelles is influenced by concentration, temperature, and pH.

Purpose of the Study:

• To investigate the micellization of sodium cholate (NaC) across a range of temperatures and pH.
• To determine the aggregation number (nmacr;) and critical micelle concentration (CMC) of NaC micelles.
• To validate a stepwise association model for NaC micelle formation.

Main Methods:

• Studied NaC micellization at temperatures 293.2–313.2 K and pH 6.0–7.2.
• Employed a stepwise association model to evaluate aggregation numbers (nmacr;).
• Utilized pyrene fluorescence to determine critical micelle concentration (CMC) and a sodium-ion-specific electrode for counterion binding.

Main Results:

• The aggregation number (nmacr;) increased with NaC concentration, supporting the stepwise association model.
• NaC aggregation numbers fluctuated with temperature, e.g., 17 at 298.2 K and 12 at 313.2 K (60 mM).
• A narrow concentration range for CMC was observed, and low counterion binding was confirmed.

Conclusions:

• The stepwise association model effectively describes NaC micellization.
• Temperature significantly impacts the aggregation number of NaC micelles.
• NaC exhibits characteristics of a weak electrolyte in solution, with limited sodium ion binding to micelles.