Determination of critical micellar concentrations of cholic acid and its keto derivatives

The critical micellar concentration (CMC) values of keto derivatives of cholic acid (3α,12α-dihydroxy-7-oxo-5β-cholanoic acid, 3α,7α-dihydroxy-12-oxo-5β-cholanoic acid, 12α-hydroxy-3,7-dioxo-5β-cholanoic acid, 3α-hydroxy-7,12-dioxo-5β-cholanoic acid, 3,7,12-triketo-5β-cholanoic acid) and cholic acid itself, were determined. Replacement of hydroxyl groups in cholic acid molecule with keto groups yields the derivatives whose CMC values increase with increase in the number of keto groups introduced. The CMCs of derivatives with the same number of keto groups but at different positions do not differ significantly. The relationship between the number of keto groups in the molecule of cholic acid keto derivatives and CMC value can be described by the following equation: CMC = 43 number of keto groups + 14.667. The effect of NaCl concentration on CMC increases with increase in the number of keto groups.