LIMITATIONS OF THE PHENOLPHTHALEIN COMPETITION METHOD FOR ESTIMATING CYCLODEXTRIN BINDING CONSTANTS

The phenolphthalein competitive spectrophotometric technique was used to obtain binding constants for cyclodextrin complexes for a variety o f both inclusates and cyclodextrins. The former included alkane-1-sulf onates (C-5-C-12), alkyl sulfates (C-6, C-8, C-12) and several heteroc yclic ligands, and the latter included beta-cyclodextrin, dimethyl-bet a-cyclodextrin and gamma-cyclodextrin. The technique was not successfu l for either alpha-cyclodextrin or trimethyl-beta-cyclodextrin inclusi on complexes, or with many primary amines and quaternary ammonium cati onic surfactants. However, for many colourless inclusates this method is a simple, convenient, reliable route to cyclodextrin binding consta nts.