Interactions between n-octyl and n-nonyl β-d-glucosides and α- and β-cyclodextrins as seen by self-diffusion NMR

In this work 1H NMR self-diffusion experiments have been performed to determine the self-diffusion coefficients of n-octyl β-d-glucoside and n-nonyl β-d-glucoside in α-cyclodextrin and β-cyclodextrin solutions at 25 °C. Two questions are addressed. The first concerns the general influence on nonionic surfactant transport properties when cyclodextrins are present in solution. The second question concerns the influence of surfactant-chain length and cyclodextrin cavity volume on the association constant. The self-diffusion coefficients of the alkyl glucosides, in cyclodextrin-containing solutions, depend on the cyclodextrin concentration on account of the formation of complexes. The cyclodextrin diffusion is only mildly influenced, since the complex has similar diffusion coefficients as the free cyclodextrin. There are some obstruction effects at the highest surfactant concentrations which decrease the cyclodextrin diffusion. A set of equations to model the self-diffusion coefficients of the surfactant and cyclodextrin was developed and is presented. On the basis of such equations, properties such as association constants, and micelle and complex diffusion coefficients can be estimated.