Micelle Formation and Testosterone Solubilization by Sodium Glycocholate

Surface tension and light-scattering studies on aqueous solutions of sodium glycocholate gave CMC values of 0.0129 and 0.0138 mole/1., respectively. Light-scattering studies in 0.1 MNaCl gave a weight-average micellar weight of about 1950, indicating that four monomers of glycocholate aggregate to form the primary micelle. Preferential broadening of the angular methyl signals in the NMR spectra suggests that glycocholate micelles are formed by back-to-back hydrophobic association of the steroid nuclei. The signal due to the glycine methylene protons in the hydrophilic region of the molecule showed little broadening. Solubility studies showed that testosterone is solubilized by glycocholate below the apparent binary CMC. The solubilizing capacity is quite low. The complex association between testosterone and glycocholate suggests mixed micelle formation.