Characterization of oligosaccharide-functionalized hyperbranched poly(ethylene imine) and their complexes with retinol in aqueous solution.

Structure, internal density distribution, and size of hyperbranched poly(ethylene imine) (PEI) functionalized with various amounts of maltose (PEI-Mal) in phosphate buffer were studied by small angle X-ray scattering (SAXS) and dynamic light scattering (DLS). The value of pH was varied in the range from 3 to 9. Virtually no effect of pH on the nanostructure was found in this interval. The SAXS results revealed a broad segmental radial density distribution, i.e. a "fluffy" globular structure rather than a distinct core-shell structure with a high-density compact core and a low-density corona. This suggests that the maltose units are rather evenly distributed both in the interior and on the surface of the species with a PEI-core of molar mass of 25,000g/mol. The DLS measurements showed that the overall size of the PEI-Mal derivatives increased as the number of maltose units in the PEI-Mal structures rises. The interaction of the hydrophobic model drug retinol with PEI or PEI-Mal derivatives was also investigated. The UV-visible spectroscopy results disclosed that the solubility of retinol in the phosphate buffer is very poor and it takes a very long time to solubilize retinol. Moreover, retinol induces aggregation of dendritic glycopolymers where the growth of aggregates occurs continuously over several days and then remains virtually constant.