Amphiphilic Cyclodextrins as Nanocarriers of Genistein: A Spectroscopic Investigation Pointing Out the Structural Properties of the Host/Drug Complex System

Nanoggregates of nonionic amphiphilic cyclodextrin (ACyD) modified with hydrophobic chains of intermediate length [(2-oligo-ethyleneoxide-6-hexylthio)-β-CyD, SC6OH] were prepared by emulsification-diffusion method. They are able to entrap an isoflavone, genistein (Gen), and the complexed species are studied at different host/guest molar ratio. The increased isoflavone solubility in the presence of the aggregates of SC6OH is investigated by UV-Vis spectroscopy, whereas size, charge, and structure of aggregates and their complexes with Gen are measured by means of static and quasi-elastic light scattering, and electrophoretic mobility measurements. On the other hand, preparing samples by the conventional method used for liposomes (hydration of an organic film of SC6OH and sonication) gives rise to aggregates with different sizes and lower colloidal stability. It is shown that the improved stability in water of ACyD aggregates both in the absence and in the presence of Gen, obtained by emulsification-diffusion is due to the existence of nanodomains of organic solvent (RH ffi 120 nm) which cannot be completely removed by evaporation and freeze-drying and in which host/guest complexes are contained. This result shows that residues of organic solvent from preparation step favor the colloidal stability of the aggregate, but their presence must be taken into account in designing systems for drug delivery.