Synthesis and monolayer behavior of amphiphilic per(2,3-di-O-alkyl)-α- and β-cyclodextrins and hexakis(6-deoxy-6-thio-2,3-di-O-pentyl)-α-cyclodextrin at an air–water interface

A synthesis of amphiphilic per(2,3-di-O-alkyl)-α- and β-cyclodextrins and hexakis(6-deoxy-6-thio-2,3-di-O-pentyl)-α-cyclodextrin and their monolayer behavior on a water surface is presented. Long alkyl chains were introduced by a treatment of the per(6-O-tert-butyldimethylsilyl) derivatives with an appropriate alkyl iodide in dimethylformamide in the presence of sodium hydride. A standard desilylation procedure followed by an iodination reaction afforded per(6-deoxy-6-iodo) analogues. In the latter reaction step, sulphur containing groups were introduced by nucleophilic substitution of the iodine with benzothiolate ion in dimethylformamide. The hexakis(6-deoxy-6-S-benzyl-2,3-di-O-pentyl)-α-cyclodextrin was transformed into extremely interesting hexakis(6-deoxy-6-thio-2,3-di-O-pentyl)-α-cyclodextrin. The surface pressure−mean molecular area (π−A) isotherms indicated that the synthesised amphiphilic cyclodextrin derivatives were capable of forming stable monolayers at the air–water interface. The shapes of the isotherms were typical for solid-like monolayers except for hexakis(6-deoxy-6-thio-2,3-di-O-pentyl)cyclomaltohexaoses which formed a more liquid monolayer.