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Physical & Chemical properties

Water solubility

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Description of key information

Key value for chemical safety assessment

Water solubility:
4.698 mg/L
at the temperature of:
25 °C

Additional information

The water solubility of 12 -ketochenodeoxycholic acid is primarily influenced by the dissociation of the ionizable polar groups. Considering the amphipathic properties of 12-ketochenodeoxycholic acid, the equilibrium of the substance in a aqueous system may be simplified as follows:

[HA]cryst.↔[HA]aq.↔ [HA]micellar↔ [A-]micellar ↔ [A-]monomeric

The protonated or undissociated species (HA) is sparingly soluble in water (4.698 mg/L at 25° C), and thus cannot form micelles. The dissociated form (A-) can exist as a monomeric form solubilized into the water medium and, above the CMC, can form micelles. Considering that the majority of bile acids have a pKa of about 5.0, at a low pH 12-ketochenodeoxycholic acid precipitate as crystalline solid and only a small concentration remain solubilized in the aqueous phase. Therefore the equilibrium is represented by [HA]cryst.↔[HA]aq.. At higher pH, instead, 12-ketochenodeoxycholic acid ionize (A-) and forms monomeric solutions below the CMC and micellar solutions above this concentration. The protonated form is more lipophilic than the ionized species and therefore can partition into a hydrophobic phase, e.g. a lipid phase or the core of micelles of the dissociated bile acid. As a consequence, at higher pH the solubility of the undissociated species (HA) is also a consequence of the repartition of HA molecules into micelles. Thus, the equilibrium of precipitation at such pH depends on the solubilizing capacity of micelles. This solubilizing capacity is low for HA alone, but the value can be increased by increasing bile salt concentration, temperature and ionic strength.

 

Igimi H and Carey MC, 1980. pH-Solubilities of chenodeoxycholic and ursodeoxycholic acids: physical-chemical basis for dissimilar solution and membrane phenomena. Journal of Lipid Research, 21, 72-90.