Types and mechanisms of solubilization

Summary Two, or possibly three, types of solubilization are shown to occur which depend on the compound being solubilized. Those systems in which the mole ratio, MR (moles material being solubilized per mole solubilizer) increases with increasing soap concentration are characterized by an increase in long X‐ray spacings to the point at which the system becomes saturated with the compound being solubilized. Hydrocarbons such as benzene, ethyl benzene, and normal paraffins fall into this class. Another type is that in which the MR remains constant above the concentration where the soap assumes its full colloidal properties, and this is characterized by no change in long X‐ray spacing. Examples of this type are soap‐soap, soap‐fatty acid, soap‐alcohol, and possibly as a subtype, soap‐dye systems. These systems are shown to be mixed micelles in which the solubilized compound is oriented with the long axis of the solubilized compound lying approximately parallel and in the plane of the long axis of the soap molecules, the hydrophylic group of both constituents being toward the water interface. Protein‐detergent complexes are discussed from the point of view of solubilization.