Inclusion complexation involving sugar-containing species: β-cyclodextrin and sugar surfactants

Abstract

Surface tension, proton NMR, and computer modeling studies were undertaken in nonionic alkylpolyglycoside (APG) solutions containing β-cyclodextrin (β-CD) with a view to characterize the inclusion complexes formed and to determine if the sugar entities of the host and guest molecules played a significant role in the process. The APGs investigated were four glucopyranosides (octyl G8, decyl G10, dodecyl G12, tetradecyl G14) and two maltosides (decyl M10, dodecyl M12). Critical micelle concentrations (CMC) were obtained in the surfactant–β-CD systems, which in all cases increased with increasing β-CD concentration. The 1:1 APG–β-CD inclusion complex was principally formed with binding constants of 425 (mol L–1)–1 for the G12 complex, 340 (mol L–1)–1 for the G10 complex, and 125 (mol L–1)–1 for the M12 complex. The preferred configuration of the G-12–β-CD complex has the surfactant tail coiled in the CD cavity with the surfactant sugar moiety sealing off the narrower opening of the CD torus.Key words: alkylpolyglycoside, β-cyclodextrin, NMR, critical micelle concentration, surface tension.