Multiple Complexation of Didecyldimethylammonium Bromide and Cyclodextrins Deduced from Electromotive Force Measurements

Abstract

The 1:1 and 1:2 macroscopic binding constants of didecyldimethylammonium bromide (DDAB) and α-, β-, and γ-cyclodextrins (CD) are determined from the electromotive force measurements with a DDAB-selective electrode, and the magnitude of these constants is interpreted in terms of the molecular structures of complexes. The 1:1 macroscopic binding constants of a double chain surfactant is 2-fold larger than that of a single chain, because the former has two chains. The 1:1 macroscopic binding constants of DDAB are in the increasing order α-CD < β-CD ≈ α-CD, consistent with those of a single chain surfactant. In the 1:1 complex of DDAB and γ-CD, one or two decyl chains are incorporated into the CD cavity. The 1:2 macroscopic binding constants of DDAB are in increasing order γ-CD ≪ β-CD α-CD. This order is interpreted in terms of the structure of complexes: the first larger ligated CD inhibits the second ligation more strongly. The present result serves for the quantitative understanding of the interaction bet...