DETERMINATION OF THE COMPLEXATION CONSTANTS BETWEEN ALKYLPYRIDINIUM BROMIDE AND ALPHA-CYCLODEXTRIN AND BETA-CYCLODEXTRIN USING ELECTROMOTIVE-FORCE METHODS

Electrochemical studies using surfactant membrane selective electrodes have shown that both alpha- and beta-cyclodextrins form 1:1 inclusion compounds with alkylpyridinium bromides (C(n)PyBr, n = 10, 12, 14, 16). For each surfactant in this homologous series the complexation constant involving alpha-cyclodextrin is always higher than the value for the corresponding beta-cyclodextrin. In addition for both cyclodextrins the complexation constants increase as the chain length of the surfactant increases, showing that the driving force dominating the formation of these complexes is the hydrophobic effect. However, it is thought that the formation of 1:2 surfactant-cyclodextrin complexes are prevented by the repulsive forces between the complexed cyclodextrin and the surfactant head group.