Studies on adsorptiochromism. I: Binding of adsorptiochromic spiropyrans to some pharmaceutically useful solids.

The adsorption of four adsorptiochromic spiropyrans to many solids (silica gel, silicic acid, fumed silica, alumina, microcrystalline cellulose, talc, titanium dioxide) was studied at 25 degrees C from cyclohexane solution. Nineteen adsorption isotherms were determined; and the binding data were fitted to the Langmuir equation. A model for binding of adsorptiochromic substances is described, and the parameters of the model are related to the experimental binding constant K.