Structural characterization of drug/hydrotalcite nanocomposites.

Hydrotalcites are inorganic layered hydroxides containing exchangeable anions, in which the lamellar plane is constituted by bivalent and trivalent metals octahedrally coordinated to six hydroxyl groups The increasing interest for these materials is due to their numerous applications in particular in catalysis and in pharmaceutical formulations. In the last case an improvement of the dissolution rate of poorly water soluble drugs and prolonged drug release may be achieved. The use of hydrotalcites for intercalating anionic sunscreens was also proposed, with the purpose of improving the sunscreen photostability. The comprehension of the structural features of these hybrid organic-inorganic materials and the transformations induced by external stimuli is fundamental to understand the stability of the materials and to identify the optimal modifications to produce improved materials and/or formulations. An hydrotalcite sample was exchanged with the anionic form of 2-phenylbenzimidazol-5-sulphonic acid (EUS), used as sun screen and the obtained nanocomposite showed interesting pharmacological properties. To elucidate the exchange and release mechanisms at the molecular level, these host-guest materials have been studied by X-ray powder diffraction also at in situ conditions, exploring the differences in the structural features of the hosting framework after the drug encapsulation and the features of the organic molecule in a confined context. The extent of the different intermolecular forces acting on the drug molecules constrained in a confined space have been investigated by Raman spectroscopy.