A Study of Cyclodextrin Complex Formation by a Freezing Point Depression Method

Abstract

The interaction and the self-association of a variety of compounds in aqueous solution were investigated by the freezing point depression method using a commercially available osmometer. This method, described in our earlier publication, was used to determine the stability constant and self-association constant, which were based on the colligative properties of solution and calculated from the decrease of osmotic pressure obtained in terms of the freezing point depression. Stability constants were measured for complexes of α-, β-, and γ-cyclodextrin with non-aromatic carbonic acids (acetic acid, formic acid, oxalic acid, succinic acid, malic acid, tartaric acid, maleic acid, citric acid), anions (I−, NO3−, CIO4−, CNO−, SCN−, Cr2O72−) and amino acids (leucine, isoleucine, methionine, phenylalanine, tryptophan), and the self-association constant for caffeine was measured. These values gave good reproducibility and rapid estimation with a simple procedure. It was concluded that the freezing point depression method is useful for estimation of the stability constant and the self-association constant for drugs in aqueous solution. © 1993, The Pharmaceutical Society of Japan. All rights reserved.