The Interactions of Vesicle-Forming Surfactants with Cyclodextrins

Abstract

Cyclodextrins (CD) are cyclic glucopyranose oligomers having a characteristic toroidal shape [1–3]. These compounds form strong host-guest complexes with many organic molecules in aqueous media because of the hydrophobic nature of the inner cavity defined by the torus. As usual in host-guest complexation, the stability of the resulting complex depends, among many other factors, on the fit of the guest molecule within the cavity provided by the host [1–3]. The three unmodified cyclodextrins are the so-called α-, s-, and γ-CD which are composed of 6, 7, and 8 glucopyranose rings respectively. α-CD, the smallest of the three hosts, has a cavity diameter of about 4 A which is ideal for binding straight alkyl chains and certain uncrowded phenyl moieties. We are particularly interested in the first type of binding because of the possibility of using cyclodextrins for the structural modification of surfactant aggregates. The interactions of surfactants with cyclodextrins have received scant attention in the literature. A few studies on the complexation of simple surfactants, like alkylsulfates or alkyltrimethylammonium salts, with α-CD and s-CD are available [4,5]. Therefore, we have recently started a research program aimed at the characterization of CD-surfactant complexes and their properties [6].