Chemical properties of bile acids: III. Bile acid structure and solubility in water

Abstract

The temperature dependence of the solubilities in water at pH 3.00 of a representative series of ten cholanoic acids (bile acids) were measured over the temperature range 10 to 50°C. The solubilities ranged from 5×10−8M for 3α-hydroxy-5β-cholanoic acid (lithocholic acid) to 2×10−3M for 3α-7β-12α-trihydroxy-5β-cholanoic acid (ursocholic acid). The solubilities increased with temperature and were found to be dependent on the number, position, and orientation of the hydroxyl groups. The hydroxyl groups affect solubility both by forming hydrogen bonds with the solvent and by reducing the hydrophobic area of the steroid nucleus. The enthalpic ΔH0 and entropic ΔS0 contributions to Δμ0 associated with the dissolution process were obtained from the temperature dependence of the solubilities. A qualitative interpretation of the thermodynamic parameters in relation to bile acid structure is also presented.