Simultaneous solubilization of steroid hormones II: androgens and estrogens.

The simultaneous solubilization of some androgens and estrogens in aqueous polysorbate 40, tetradecyltrimethylammonium bromide, and sodium lauryl sulfate was studied. The solubilizations of estradiol and testosterone were independent of each other in all three association colloids. However, if the estrogen component was ethinyl estradiol, the solubilization was dependent on the addition order. The estrogen precipitates more readily than testosterone in polysorbate 40 and tetradecyltrimethylammonium bromide, but the opposite is true in sodium lauryl sulfate. The simultaneous solubilizations of methyltestosterone or ethisterone with the estrogens tested were different from those of testosterone. The solubilization behavior of the steroids is discussed, starting with the pseudophase model and different solubilization loci. Results indicated that the free energy change of micellar binding, delta Gb, decreases with increased steroid polarity. The simultaneous solubilization cannot be predicted by delta Gb but may be explained by differences in the solubilization mechanism.