Structural properties of several amphiphile cyclodextrins and some related nanospheres. An X-ray scattering and freeze-fracture electron microscopy study

Amphiphilic cyclodextrins bearing fatty acyl chains covalently linked to their secondary hydroxyl groups are able to form nanospheres with an internal organization. The structure of several cyclodextrins with different acyl chain lengths (CD-Cn) was investigated using X-ray scattering and freeze fracture electron microscopy. From the experimental data and using physicochemical arguments; we propose structure models. beta CD-C6, beta CD-C8, beta CD-C10, beta CD-C12, and gamma CD-C14 form polar columns, surrounded by the paraffin chains, and associated in a 2-D hexagonal lattice. The structure of alpha CD-C14 and beta CD-C14 is body-centered cubic; it comprises one lattice of dimers aligned along the edges of the cubic cell and a second identical lattice with a translation of the half in the three directions. This results in the formation of two globules, one at the apex and one at the center of the cell. The structures are unusual for cyclodextrin molecules; they result from the presence of the numerous paraffin chains linked to each molecule. Indeed, the structures are reminiscent of those found in lipid systems.