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The solubility of testosterone at 25° was determined in aqueous solutions containing varying concentrations of dodecyltrimethylammonium bromide (DTAB), hexadecyl-trimethylammonium bromide (HTAB), and potassium laurate (KL). After the initial stages of solubilization, a linear relationship was observed between the amount of testosterone solubilized and the molar concentration of the surfactant. The order of increasing solubilizing capacity was DTAB < HTAB < KL. The environment of solubilized testosterone, as investigated by the Z-value method, was found to be quite polar in all cases. At low concentrations of DTAB and HTAB the Z value was similar to that in water. As the concentration of the quaternary ammonium bromides increased, a precipitous drop in Z value, corresponding to a sudden decrease in environmental polarity, was observed in the region of the critical micelle concentration. With further increase in the concentration of DTAB and HTAB the Z value remained reasonably constant. In low KL concentrations the Z value of the testosterone environment was higher (more polar) than in water. With increasing concentrations of KL the Z value displayed behavior similar to that in DTAB and HTAB. In general, solutions of ionic surfactants showed higher Z values than those of the nonionic surfactants examined previously.

Methylene blue is adsorbed by potato starch from aqueous solution as a monomer or dimer, depending upon its concentration. The adsorption phenomenon can be described by the Langmuir equation. The effect of methanol, dioxane, sucrose, and urea on methylene blue adsorption has been examined. These water-miscible additives shift the monomer-dimer equilibrium of the dye in the direction of the monomer and reduce the extent of methylene blue adsorption without significantly affecting the maximum possible adsorption. This appears to indicate that their effect is primarily on the effective concentration of the dye. At high concentrations, methanol and dioxane apparently further reduce adsorption by affecting the surface of potato starch.

The solution behavior of testosterone was studied with a view toward explaining an anomalous initial supersaturation observed in solubilized systems containing testosterone. This anomalous behavior was related to the conversion of an anhydrous crystal form of testosterone to a hydrate crystal form. The solution behavior of the anhydrous form was studied in several concentrations of polysorbate 20, dodecyltrimethylammonium bromide, and potassium laurate. In low concentrations of polysorbate 20 and potassium laurate, the time required to attain the solubility peak was less than that in distilled water. An increase in surfactant concentration resulted in a decrease in the solubility peak time. At higher concentrations, dodecyltrimethylammonium bromide exhibited a pattern similar to that of polysorbate 20 and potassium laurate; at a low concentration, however, a prolongation of the peak solubility time was noted.

The solubility of testosterone in aqueous solutions of partially purified polysorbate 20, 40, and 60 was determined by measuring the area under the ultraviolet spectral peaks. There was solubilization below the critical micelle concentration. A linear relationship was observed between the amount of testosterone solubilized and the per cent polysorbate concentration. Polysorbate 60 exhibited the greatest solubilizing capacity and polysorbate 20 the least. The Z-value method for determining solvent polarity was employed to investigate the polarity of the environment in which testosterone was solubilized. At low polysorbate concentrations the Z-value was similar to that in water. As the polysorbate concentration increased, the Z-value decreased. This decrease in Z-value paralleled the increase in solubility of testosterone.

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.