Taurocholate and taurodeoxycholate: gel formation and protonation constants

Area of Science:

• Biochemistry
• Physical Chemistry
• Colloid Science

Background:

• Bile acids like taurocholate (TC) and taurodeoxycholate (TDC) form micellar aggregates in aqueous solutions.
• The role of hydrogen ions in the protonation of these bile acids and their micellar structures is not fully understood.
• Gel formation during experiments with bile acids has been observed but not adequately addressed, impacting reproducibility.

Purpose of the Study:

• To investigate the micellar properties of taurocholate (TC) and taurodeoxycholate (TDC) in aqueous solutions.
• To determine whether hydrogen ions contribute to micellar aggregates or directly protonate the bile acid molecules.
• To quantify the protonation constants of TC and TDC under specific ionic conditions.

Main Methods:

• Electromotive force (EMF) measurements using a galvanic cell with a glass electrode.
• Experiments conducted at 25°C in a 1.00 mol dm⁻³ NaCl ionic medium.
• Analysis of protonation phenomena in the presence of sodium and hydrogen ions.

Main Results:

• Protonation constants were determined for TC (log k1 = 0.07 ± 0.02) and TDC (log k'1 = 1.60 ± 0.03).
• The study highlights the issue of gel formation, which can compromise experimental reproducibility due to non-equilibrium conditions.
• Distinguishes between protonation of the bile acid anions and their aggregation into micelles.

Conclusions:

• The determined protonation constants provide quantitative data on the behavior of TC and TDC.
• The findings suggest that gel formation is a critical factor affecting the reliability of experiments involving bile acid solutions.
• Clarifies the protonation behavior of TC and TDC, contributing to a better understanding of bile acid-water interactions.